ISO 24509:2019
(Main)Ergonomics — Accessible design — A method for estimating minimum legible font size for people at any age
Ergonomics — Accessible design — A method for estimating minimum legible font size for people at any age
This document provides a method for estimating minimum legible font size for single characters, but not for words or sentences, in self-luminous or reflected mode, used in documents, products labels, signs, and displays for people at any age and in any viewing condition in which viewing distance, luminance and contrast are varied. This document applies designing and evaluating legibility of single characters for people at any age who have no pathological disorders in their eyes, but not for people with visual impairments such as low vision. The application is specifically directed to, but not limited to, the cases of printed materials where fixed font size is used. Applicability of the method to other languages is given in Annex F.
Ergonomie — Conception accessible — Taille de police lisible minimale pour les personnes de tout âge
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 24509
First edition
2019-10
Ergonomics — Accessible design —
A method for estimating minimum
legible font size for people at any age
Ergonomie — Conception accessible — Taille de police lisible
minimale pour les personnes de tout âge
Reference number
ISO 24509:2019(E)
©
ISO 2019
---------------------- Page: 1 ----------------------
ISO 24509:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 24509:2019(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Application conditions . 2
5 Estimation of minimum legible font size . 2
6 Correction by contrast effect . 3
Annex A (normative) Visual acuity data as a function of age and viewing distance .5
Annex B (normative) Luminance correction coefficient to visual acuity . 7
Annex C (informative) Calculation example of the minimum legible font size at a given
viewing condition . 8
Annex D (informative) Minimum legible font size calculated for variable age and viewing
distance at constant luminance levels for reference .10
Annex E (informative) Practical application to a group of people with a range of age and
viewing conditions .25
Annex F (informative) Application to non-alphabetical characters: Korean, Chinese and
Thai languages .27
Annex G (informative) Data and principle of the method for estimating minimum legible
font size .29
Annex H (informative) Scaling of legibility using minimum legible font size .35
Bibliography .37
© ISO 2019 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 24509:2019(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see
www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 4,
Ergonomics of human-system interaction.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO 2019 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 24509:2019(E)
Introduction
Characters are widely used almost every time displays, documents, and other media for visual
information are involved. Accessibility to printed or displayed text is one of the critical issues in this
age of mass information, especially for older people. However, methods for designing and evaluating
the legibility of characters have not been well established yet.
Most of the problems with legibility are concerned with appropriate font size to read text in various
conditions. This problem is worse for older people whose visual acuity decreases with age, especially
at near viewing distances. Provision of legible characters to older people at any viewing condition is
becoming more important to enhance safety and comfort in their social activities.
The legibility of text has two major problems. One is concerned with legibility of single characters
and the other one is for words and sentences where inter-character spacing or inter-line spacing is
additionally investigated. The former one is the basic problem of legibility and can be extended to the
legibility for words or sentences.
While there exist many factors that affect legibility of single characters, a limited number of critical
factors can be identified as vision-related ones, which include age of the viewer, viewing distance,
luminance and contrast. A method for estimating legible font size using these critical factors can
be developed and generally applied to a wide range of practical cases. There can exist other critical
factors concerning with physical aspects of presenting characters such as display characteristics and
[1]
their environments , but these effects can be evaluated once the basic method based on human vision
factors is established.
The legibility for people who have pathological disorders like low vision are not addressed in this
document due to a lack of scientific resources as well as due to large individual differences in visual
abilities among people with different types of impairments.
[2]
This document is based on principles of accessible design from ISO/IEC Guide 71 and on data from
[3]
ISO/TR 22411 .
© ISO 2019 – All rights reserved v
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 24509:2019(E)
Ergonomics — Accessible design — A method for
estimating minimum legible font size for people at any age
1 Scope
This document provides a method for estimating minimum legible font size for single characters, but not
for words or sentences, in self-luminous or reflected mode, used in documents, products labels, signs,
and displays for people at any age and in any viewing condition in which viewing distance, luminance
and contrast are varied.
This document applies designing and evaluating legibility of single characters for people at any age
who have no pathological disorders in their eyes, but not for people with visual impairments such as
low vision. The application is specifically directed to, but not limited to, the cases of printed materials
where fixed font size is used.
Applicability of the method to other languages is given in Annex F.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 24502, Ergonomics — Accessible design — Specification of age-related luminance contrast for
coloured light
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
visual acuity
V
capacity for seeing distinctly fine details that have very small angular separation
any of a number of measures of spatial discrimination such as the reciprocal of the
value of the angular separation in minutes of arc of 2 neighbouring objects (points or lines or other
specified stimuli) which the observer can just perceive to be separate
[SOURCE: CIE S 017/E:2011]
3.2
viewing distance
D
distance between the eye and the object to look at
Note 1 to entry: Expressed in meters in this document.
© ISO 2019 – All rights reserved 1
---------------------- Page: 6 ----------------------
ISO 24509:2019(E)
3.3
luminance correction coefficient
coefficient for correcting the effect of luminance on visual acuity (3.1) relative to the acuity at the
2
100 cd/m level
3.4
minimum legible font size
character size, expressed in unit of point, for a single character under which the character is not legible
with less than 80 % probability at the specific viewing condition
Note 1 to entry: The unit of point is defined in this document as 1 pt = 0,351 4 in, which is used mainly in the US
and Japan. Another definition is 1 pt = 1/72 inch = 0,352 77 in, mainly used in the EU. The difference is too small
to have any influence on legibility.
Note 2 to entry: Minimum legible font size is a baseline of legibility and not at the comfort level of legibility (see
Annex H)
4 Application conditions
For the application of the method for estimating the minimum legible font size, the following viewing
conditions shall be specified:
a) age: the age of a person shall be from 6 years old to 90 years old;
b) viewing distance: the viewing distance shall be between 0,2 m and 100 m;
2 2
c) luminance: the luminance shall be between 0,01 cd/m and 3 000 cd/m .
NOTE Luminance means the luminance of the surrounding area, not of the font, for the positive font
type where a character looks darker than the background. In case of negative font type, where a character
looks lighter than the surrounding area, luminance means that of the character.
d) contrast: the contrast, positive or negative, shall be between 0 % and 100 %, defined by Michaelson
Contrast (see NOTE in Clause 6).
5 Estimation of minimum legible font size
The minimum legible font size shall be calculated by the following procedure. Calculation examples and
application are given in Annexes C, D and E.
2
a) Select a visual acuity, V , at the luminance level of 100 cd/m for a specified observer’s age and for a
0
specified viewing distance from Annex A.
2
b) Select a luminance correction coefficient, k, for a specified luminance, L (in cd/m ), of the viewing
condition from Annex B, and correct visual acuity to the one under the specified luminance using
Formula (1).
Vk= V (1)
0
where
V is a visual acuity under the specified viewing condition;
k is a luminance correction coefficient;
2
V is the visual acuity at the luminance of 100 cd/m .
0
c) Calculate a size factor, S, using Formula (2).
2 © ISO 2019 – All rights reserved
---------------------- Page: 7 ----------------------
ISO 24509:2019(E)
SD= V (2)
where
S is the size factor;
D is the viewing distance (m);
V is the visual acuity under the specified viewing condition.
d) Calculate the minimum legible font size, P (in points), using Formula (3) with the size factor and
min
coefficients given in Table 1 (see Annex G).
Pa=+Sb (3)
min
where
P is a minimum legible font size (in points);
min
S is the size factor;
a and b are the formula coefficients given in Table 1.
Table 1 — Formula coefficients a and b in Formula (3)
Font type a b
Serif 8,2 2,6
Sans-serif 6,4 3,0
6 Correction by contrast effect
Formula (3) is based on the ideal case in which the contrast between character and background is
100 %. For practical cases where the contrast is less than 100 %, P obtained in Formula (3) shall be
min
corrected by Formula (4) using a contrast correction coefficient, r, given in Table 2 (see Annex G).
Pr= P (4)
min,c min
where
P is the contrast corrected minimum legible font size (in points);
min,c
r is the contrast correction coefficient.
Table 2 — Contrast correction coefficients (font size multiplier) for different contrast levels in
positive and negative contrast
Contrast Positive-contrast Negative-contrast
100 1,00 1,00
90 1,04 1,05
80 1,09 1,11
70 1,15 1,18
60 1,23 1,28
50 1,33 1,40
© ISO 2019 – All rights reserved 3
---------------------- Page: 8 ----------------------
ISO 24509:2019(E)
Table 2 (continued)
Contrast Positive-contrast Negative-contrast
40 1,46 1,57
30 1,66 1,84
20 2,01 2,32
10 2,89 3,68
5,0 4,45 6,62
2,5 7,75 17,99
For a coloured character and a background, the estimation of contrast shall follow ISO 24502.
NOTE Contrast in Table 2 is the modulation contrast defined as (L − L )/(L + L ) where L and
max mim max min max
L mean the higher and the lower luminance of the modulation. The positive contrast means that luminance of
min
a character is lower than that of the surrounding area and the negative-contrast is the opposite.
4 © ISO 2019 – All rights reserved
---------------------- Page: 9 ----------------------
ISO 24509:2019(E)
Annex A
(normative)
Visual acuity data as a function of age and viewing distance
A.1 Data table for visual acuity
Table A.1 provides numerical data of visual acuity for variable age of an observer and viewing distance
2
at the reference luminance level of 100 cd/m . Age is expressed in year and given in rows, and viewing
[5]
distance is expressed in meter and given in columns. Data are taken from JIS S 0032 and extrapolated
to 6 years and to 90 years of age.
Table A.1 — Visual acuity as a function of age and viewing distance
Viewing distance
Age
m
years
0,2 0,3 0,5 1 2 3 5 10 20 30 50 100
6 1,498 1,621 1,726 1,810 1,853 1,867 1,879 1,871 1,866 1,865 1,864 1,863
8 1,361 1,512 1,645 1,752 1,808 1,827 1,842 1,831 1,825 1,823 1,822 1,821
10 1,237 1,411 1,567 1,696 1,764 1,787 1,806 1,792 1,785 1,783 1,781 1,779
12 1,125 1,316 1,493 1,641 1,721 1,748 1,770 1,754 1,746 1,743 1,741 1,739
14 1,022 1,228 1,423 1,589 1,679 1,710 1,735 1,717 1,707 1,704 1,701 1,700
16 0,929 1,146 1,356 1,538 1,638 1,672 1,701 1,680 1,669 1,666 1,663 1,661
18 0,844 1,069 1,292 1,488 1,598 1,636 1,667 1,644 1,633 1,629 1,626 1,623
20 0,767 0,998 1,231 1,441 1,559 1,600 1,634 1,609 1,597 1,593 1,589 1,587
22 0,697 0,931 1,173 1,395 1,521 1,565 1,602 1,575 1,562 1,557 1,553 1,551
24 0,634 0,869 1,117 1,350 1,484 1,531 1,570 1,542 1,527 1,522 1,518 1,516
26 0,576 0,810 1,065 1,307 1,448 1,498 1,539 1,509 1,493 1,488 1,484 1,481
28 0,524 0,756 1,015 1,265 1,412 1,465 1,509 1,477 1,461 1,455 1,451 1,448
30 0,476 0,706 0,967 1,224 1,378 1,433 1,479 1,445 1,428 1,423 1,418 1,415
32 0,433 0,658 0,921 1,185 1,344 1,402 1,450 1,415 1,397 1,391 1,386 1,383
34 0,393 0,614 0,878 1,147 1,311 1,371 1,421 1,384 1,366 1,360 1,355 1,352
36 0,357 0,573 0,836 1,110 1,279 1,341 1,393 1,355 1,336 1,330 1,325 1,321
38 0,325 0,535 0,797 1,075 1,248 1,312 1,366 1,326 1,307 1,300 1,295 1,291
40 0,295 0,499 0,759 1,040 1,218 1,284 1,339 1,298 1,278 1,271 1,266 1,262
42 0,268 0,465 0,723 1,007 1,188 1,256 1,312 1,270 1,250 1,243 1,237 1,233
44 0,244 0,434 0,689 0,975 1,159 1,228 1,286 1,243 1,222 1,215 1,209 1,205
46 0,222 0,405 0,657 0,944 1,131 1,201 1,261 1,217 1,195 1,188 1,182 1,178
48 0,201 0,378 0,626 0,913 1,103 1,175 1,236 1,191 1,169 1,161 1,156 1,151
50 0,183 0,353 0,596 0,884 1,076 1,149 1,211 1,166 1,143 1,136 1,130 1,125
52 0,166 0,329 0,568 0,856 1,050 1,124 1,187 1,141 1,118 1,110 1,104 1,100
54 0,151 0,307 0,541 0,828 1,025 1,100 1,164 1,117 1,093 1,085 1,079 1,075
56 0,137 0,287 0,516 0,802 1,000 1,076 1,141 1,093 1,069 1,061 1,055 1,050
58 0,125 0,267 0,492 0,776 0,975 1,052 1,118 1,070 1,046 1,038 1,031 1,027
60 0,114 0,249 0,468 0,751 0,951 1,029 1,096 1,047 1,022 1,014 1,008 1,003
© ISO 2019 – All rights reserved 5
---------------------- Page: 10 ----------------------
ISO 24509:2019(E)
Table A.1 (continued)
Viewing distance
Age
m
years
0,2 0,3 0,5 1 2 3 5 10 20 30 50 100
62 0,103 0,233 0,446 0,727 0,928 1,007 1,075 1,025 1,000 0,992 0,985 0,981
64 0,094 0,217 0,425 0,704 0,906 0,985 1,053 1,003 0,978 0,970 0,963 0,958
66 0,085 0,203 0,405 0,681 0,884 0,964 1,033 0,982 0,956 0,948 0,942 0,937
68 0,077 0,189 0,386 0,660 0,862 0,942 1,012 0,961 0,935 0,927 0,920 0,915
70 0,070 0,176 0,368 0,638 0,841 0,922 0,992 0,940 0,915 0,906 0,900 0,895
72 0,064 0,165 0,351 0,618 0,821 0,902 0,973 0,920 0,895 0,886 0,879 0,874
74 0,058 0,154 0,334 0,598 0,800 0,882 0,953 0,901 0,875 0,866 0,860 0,855
76 0,053 0,143 0,318 0,579 0,781 0,863 0,935 0,882 0,856 0,847 0,840 0,835
78 0,048 0,134 0,303 0,560 0,762 0,844 0,916 0,863 0,837 0,828 0,821 0,816
80 0,044 0,125 0,289 0,543 0,743 0,826 0,898 0,844 0,818 0,810 0,803 0,798
82 0,040 0,116 0,275 0,525 0,725 0,808 0,880 0,826 0,800 0,792 0,785 0,780
84 0,036 0,109 0,262 0,508 0,708 0,790 0,863 0,809 0,783 0,774 0,767 0,762
86 0,033 0,101 0,250 0,492 0,690 0,773 0,846 0,792 0,765 0,757 0,750 0,745
88 0,030 0,095 0,238 0,476 0,673 0,756 0,829 0,775 0,748 0,740 0,733 0,728
90 0,027 0,088 0,227 0,461 0,657 0,739 0,813 0,758 0,732 0,723 0,717 0,712
6 © ISO 2019 – All rights reserved
---------------------- Page: 11 ----------------------
ISO 24509:2019(E)
Annex B
(normative)
Luminance correction coefficient to visual acuity
B.1 Data table for luminance correction coefficient
Table B.1 provides the luminance correction coefficient which is used to obtain visual acuity at different
2
level of luminance from the reference level of 100 cd/m by using Formula (1). Table B.1 is given for the
2 2 [5]
luminance range from 0,01 cd/m to 3 000 cd/m . Data are taken from JIS S 0032 .
2
Table B.1 — Relative visual acuity as a function of luminance normalized at the 100 cd/m level
(luminance correction coefficient)
Luminance Luminance Luminance Luminance
correction correction
2 2
cd/m cd/m
coefficient coefficient
0,01 0,028 10 0,757
0,02 0,101 20 0,830
0,03 0,144 30 0,873
0,04 0,174 40 0,903
0,05 0,198 50 0,927
0,06 0,217 60 0,946
0,07 0,233 70 0,962
0,08 0,248 80 0,977
0,09 0,260 90 0,989
0,1 0,271 100 1,000
0,2 0,344 200 1,036
0,3 0,387 300 1,057
0,4 0,417 400 1,072
0,5 0,441 500 1,083
0,6 0,460 600 1,093
0,7 0,476 700 1,101
0,8 0,491 800 1,108
0,9 0,503 900 1,114
1 0,514 1 000 1,119
2 0,587 2 000 1,155
3 0,630 3 000 1,176
4 0,660
5 0,684
6 0,703
7 0,719
8 0,734
9 0,746
© ISO 2019 – All rights reserved 7
---------------------- Page: 12 ----------------------
ISO 24509:2019(E)
Annex C
(informative)
Calculation example of the minimum legible font size at a given
viewing condition
C.1 General
This annex provides a calculation example of a minimum legible font size for a given viewing condition
using the method described in Clauses 5 and 6.
An alphanumeric character of the serif font seen by a 68-year-old person at a viewing distance of 50 cm
2
and a luminance of 10 cd/m with a positive contrast of 30 % is taken as a case for this calculation.
C.2 Example of calculation
An alphanumeric character of serif font seen by a 68-year-old person in the conditions of Table C.1 is
taken as an example for calculating the minimum font size.
Table C.1 — Viewing conditions for a calculation example
Viewing condition Specification
Age 68 years
Viewing distance 50 cm
2
Luminance level 10 cd/m
30 %, positive
Contrast
(in Michelson contrast)
According to the method described in Clause 5, visual acuity of the observer (68 years old) at the 50 cm
2
viewing distance for the reference condition (100 cd/m ), V , is taken from Table A.1 as Formula (C.1):
0
V =0,386 (C.1)
0
2
This visual acuity is corrected to the 10 cd/m luminance level by using the luminance correction
coefficient of k = 0,757, taken from Table B.1, as Formula (C.2):
Vk==V 0,,757×=0 386 0,292 (C.2)
0
With this visual acuity, V, and the viewing distance, D, in meters, the size factor, S, can be calculated
with Formula (C.3):
SD==V 05,,0 292=17, 1 (C.3)
8 © ISO 2019 – All rights reserved
---------------------- Page: 13 ----------------------
ISO 24509:2019(E)
By using coefficients from Table 1 for the serif font characters (a = 8,2; b = 2,6), a minimum legible font
size (at the 100 % contrast condition) is calculated with Formula (C.4):
Pa=+Sb=×82,,1712+=,,6166 (C.4)
min
This font size is finally corrected to the condition of 30 % contrast by using contrast correction
coefficient, r = 1,66 (for positive contrast), taken from Table 2 as Formula (C.5):
Pr==P 16,,61×=66 27,6 pt (C.5)
()
min,c min
A font size of 27,6 points is the minimum legible size for this example including the contrast correction.
C.3 In case of wearing spectacles or contact lenses
The above example is based on the assumption that no spectacles or contact lenses are used. However,
older people usually wear spectacles or contact lenses of various kinds. Because the extent of those
optical corrections largely varies depending on individuals’ preferences, it is difficult to estimate visual
acuity of those people. However, in case that visual acuity of those persons is known preferably at the
viewing condition in question, it is possible to calculate the minimum legible font size from step (c)
using Formula (3).
For example, if a person in the example of C.2 wears his/her glasses and improves his/her visual acuity
from 0,292 to 0,8 at the viewing condition, then Formulae (C.6) to (C.8) can apply.
SD==V 05,,08=0,625 (C.6)
Pa=+Sb=×82,,0 625+=26,,773 (C.7)
min
Pr==P 16,,67×=73 12,8 pt (C.8)
()
min,c min
A font size of 12,8 points is the minimum legible size for that person when he/she wears spectacles.
NOTE If visual acuity of a person wearing spectacles is known at a luminance level that differs from the
viewing condition in question, luminance correction is needed by referring to Table B.1.
© ISO 2019 – All rights reserved 9
---------------------- Page: 14 ----------------------
ISO 24509:2019(E)
Annex D
(informative)
Minimum legible font size calculated for variable age and viewing
distance at constant luminance levels for reference
D.1 General
This annex provides calculation results of minimum legible font size as reference data for several
sampling points of viewing distance and for age from 10 years to 90 years in 10-year steps at five
2 2 2 2 2
constant luminance levels of 1 000 cd/m , 100 cd/m , 10 cd/m , 1 cd/m , and 0,1 cd/m . These data are
used as reference data of minimum legible font size at some viewing conditions, and they can be used
with interpolation or extrapolation to estimate the font size at intermediate or external range of those
sampling points.
The data is calculated at the highest contrast level (100 %) and the contrast correction is required for
lower contrast than 100 % according to the method described in Clause 6. The data are available for a
serif font as well as for a sans-serif font.
D.2 Minimum legible font size data calculated for some sampling points of
viewing conditions
Each of the Figures D.1 to D.5 shows the minimum legible font size calculated for several sampling points
of viewing distance (0,3 m, 0,5 m, 1 m, 2 m, 5 m, and 10 m) and for nine different ages from 10 years to
90 years in 10-years steps. Figures D.1 to D.5 correspond to different luminance levels from 1 000 cd/
2 2 2
m to 0,1 cd/m respectively in one logarithmic unit steps. Approximately, the 1 000 cd/m level can be
2
used for the outdoor condition under sunshine, the 100 cd/m level for normal indoor environment in
2 2
good lighting condition, the 10 cd/m level for indoor in poor lighting condition, the 1 cd/m level for
2
dim lighting, and the 0,1 cd/m level for a dark room where walking becomes difficult.
For Figures D.1 to D.5 the following key applies:
Key
X viewing distance (m)
Y minimum legible font size (pt)
90 years
80 years
70 years
60 years
50 years
40 years
30 years
20 years
10 years
10 © ISO 2019 – All rights reserved
---------------------- Page: 15 ----------------------
ISO 24509:2019(E)
a) Serif font b) Sans-serif font
Figure D.1 — Calculated minimum legible font size as a function of viewing distance for
2
different ages from 10 years to 90 years in 10-years steps. Luminance level is 1 000 cd/m
a) Serif font b) Sans-serif font
Figure D.2 — Calculated minimum legible font size as a function of viewing distance for
2
different ages from 10 years to 90 years in 10-year steps. Luminance level is 100 cd/m
© ISO 2019 – All rights reserved 11
---------------------- Page: 16 ----------------------
ISO 24509:2019(E)
a) Serif font b) Sans-serif font
Figure D.3 — Calculated minimum legible font size as a function of viewing distance for
2
different ages from 10 years to 90 years in 10-year steps. Luminance level is 10 cd/m
a) Serif font b) Sans-serif font
Figure D.4 — Calculated minimum legible font size as a function of viewing distance for
2
different ages from 10 years to 90 years in 10-year steps. Luminance level is 1 cd/m
12 © ISO 2019 – All rights reserved
---------------------- Page: 17 ----------------------
ISO 24509:2019(E)
a) Serif font b) Sans-serif font
Figure D.5 — Calculated minimum legible font size as a function of viewing distance for
2
different ages from 10 years to 90 years in 10-year steps. Luminance level is 0,1 cd/m
Numerical values of Figures D.1 to D.5 are presented in Tables D.1 to D.10. The range of age and viewing
distance are expanded in the tables for reference.
A calculation tool for a single minimum legible font size for a given parameters (age, viewing distance,
[6]
and luminance) is provided by AIST, Japan .
2
Table D.1 — Minimum legible font size for a serif font at the 1 000 cd/m level [see Figure D.1 a)]
Viewing distance
Age
m
years
0,2 0,3 0,5 1 2 3 5 10 20 30 50 100
6 3,6 4,0 4,7 6,6 10,5 14,4 22,1 41,8 81,1 120,5 199,2 395,9
8 3,7 4,1 4,8 6,8 10,7 14,6 22,5 42,6 82,9 123,2 203,7 405,0
10 3,8 4,2 4,9 6,9 10,9 14,9 22,9 43,5 84,7 125,9 208,3 414,5
12 3,9 4,3 5,1 7,1 11,1 15,2 23,3 44,4 86,5 128,7 213,1 424,0
14 4,0 4,4 5,2 7,2 11,3 15,5 23,7 45,3 88,5 131,6 218,0 433,7
16 4,2 4,5 5,3 7,4 11,5 15,7 24,1 46,2 90,4 134,6 222,9 443,8
18 4,3 4,7 5,4 7,5 11,8 16,0 24,6 47,2 92,3 137,6 227,9 454,1
20 4,5 4,8 5,6 7,7 12,0 16,3 25,0 48,1 94,4 140,6 233,2 464,4
22 4,7 5,0 5,7 7,9 12,2 16,6 25,5 49,1 96,4 143,8 238,5 475,1
24 4,9 5,1 5,9 8,0 12,5 17,0 25,9 50,1 98,6 147,0 244,0 486,0
26 5,1 5,3 6,0 8,2 12,7 17,3 26,4 51,2 100,8 150,3 249,5 497,4
28 5,4 5,5 6,2 8,4 13,0 17,6 26,9 52,2 102,9 153,7 255,1 508,7
30 5,7 5,7 6,4 8,6 13,2 17,
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.