ISO/IEC 25986:2026

• Abstract:

  This document specifies the set of definitions, rules and guidelines for applying the Nesma Easy Functional Sizing method.

• Status: Published
• Publication Date: 26-Jul-2026
• ICS: 35.080 - Software
• Technical Committee: ISO/IEC JTC 1 - Information technology
• Drafting Committee: ISO/IEC JTC 1 - Information technology
• Current Stage: 6060 - International Standard published
• Start Date: 27-Jul-2026
• Due Date: 10-Jun-2027
• Completion Date: 27-Jul-2026

ISO/IEC 25986:2026 is an International Standard published by ISO and IEC for software engineering. It specifies the definitions, rules and guidelines for applying the Nesma Easy Functional Sizing (EFS) method. The method measures the functional size of an automated information system from the user’s perspective, and it is intended for anyone who needs to determine that size in a consistent way.

What does ISO/IEC 25986:2026 specify?

ISO/IEC 25986:2026 specifies how to measure functional size with the Nesma Easy Functional Sizing (EFS) method. It applies to automated information systems and to all functional domains named in ISO/IEC TR 14143-5:2004.

The standard focuses on sizing only. It does not deal with productivity, quality standards, budget building or other metrics that may use functional size as an input.

The document is organized as follows:

Part of the document	What it covers
Clause 1	Scope, conformity, applicability and focus
Clause 2	Description of EFS, users, system boundary, components, functional size and naming
Clause 3	Practical situations and counting guidance
Appendix A	Difference between high-level FPA and Easy Functional Sizing
Appendix B	Definitions

What are the key requirements of ISO/IEC 25986:2026?

ISO/IEC 25986:2026 defines EFS as an objective way to size the functionality offered to the user by an information system. In practice, that means the count is based on what the system does for users, not on the technical solution, platform or implementation style.

Measure from the user’s point of view

Clause 2 says the measurement is based on functional user requirements. Only functionality requested by the user and recognizable as meaningful to the user is included.

This matters because teams should count business-visible behavior, not internal design choices. A web screen, API, batch job or database design can all be part of one user function if they deliver the same user-visible result.

Define the users and the system boundary first

Clause 2.1 identifies three user types: people or organizations using the system, the owner or Product Owner, and other information systems. The standard also says the analysis should be done with users or at least verified with them.

Clause 2.1.2 makes the system boundary a key decision. That boundary determines which data movements cross into or out of the measured system, so it directly affects the functional size.

Count only three kinds of user functions

Clause 2.2 maps user functions to three EFS components: Logical File (LF), External Input (EI) and External Output (EO). The standard assigns fixed function-point weights to these component types in the function point table in Clause 2.3.

In practice, this simplifies counting. Instead of many detailed categories, the analyst decides whether each user function is a stored logical group, an input that changes data, or an output that presents data.

Apply the rules for logical files, inputs and outputs

Clause 2.2.1 says a Logical File is a logical group of permanent data from the user’s perspective that is used and/or maintained by the system. Physical tables may be combined into one Logical File if users see them as one meaningful unit.

Clause 2.2.2 says an External Input is a complete process whose main purpose is to add, change or delete data in one or more Logical Files. An External Output is a complete process whose main purpose is to present data to a user or another system.

This distinction matters because many real functions combine interface, business rules and storage. EFS counts the whole user transaction once, based on its primary purpose.

Use the practical counting rules in Clause 3

Clause 3 gives the working rules for common situations. It says not to count at screen or tab level, and not to count functions that were built but not specified by users.

For Logical Files, Clause 3.1 explains entity dependence and entity independence. The user interaction decides whether related physical tables count as one Logical File or several, especially when deleting one side automatically removes the related data.

For External Inputs and External Outputs, Clauses 3.3 and 3.4 separate the purpose of the function. Inputs change stored data; outputs present data, including to another information system. Different media alone do not create a new output, and user selection options are not counted as separate functions.

Treat support functions carefully

Clause 3.5 says some general support features are not counted separately, including menu structures, navigation, generic login, report generator, error messages, multilingualism, refresh, cancel, close, filtering and sorting.

The same clause also gives special rules for help functions, FPA tables, mutation logging and security. This matters in real counting work because these features are common and can otherwise be overcounted or counted inconsistently.

Distinguish product size and project size

Clause 2.4 defines product size as the size of the delivered information system and project size as the size of new development or enhancement work. Product size changes when functionality is added or removed; project size sums the added, modified and deleted user functions in a change effort.

This distinction is important in contracts and planning. A team may measure the same system as one product size, but several project sizes across multiple releases or sprints.

What terms does ISO/IEC 25986:2026 define?

• Easy Functional Sizing (EFS) - A method for measuring the size of the functionality offered to the user by an information system, independent of quality and technical requirements.
• Functional size - The size derived by quantifying Functional User Requirements through the total number of function points.
• Logical File (LF) - A logical grouping of permanent data from the user’s perspective that is used and/or maintained by the system.
• External Input (EI) - A unique user function where data or control information from outside the application enters the application and causes data to be added, changed or deleted.
• External Output (EO) - A unique output recognized by the user that crosses the system boundary.
• Function point - The unit used to express the size of an information system or a project.
• System boundary - The conceptual interface between the information system being measured and its users and/or other information systems.
• FPA table - An entity type with a secondary function, such as constants, texts or decodings, whose data is maintainable.

Who uses ISO/IEC 25986:2026?

ISO/IEC 25986:2026 is for anyone involved in determining functional size. The foreword says it is intended to help a novice user perform a size measurement independently and consistently.

In practice, it is useful for:

• Product Owners and their representatives who define functionality
• end-users, functional administrators and operators who can confirm what the system should do
• analysts and estimators who need a functional size for effort, cost or capacity planning
• software delivery teams working in Agile or DevOps environments
• people who compare delivered functionality across releases, projects or suppliers

The standard is especially relevant when functional size is used as a basis for estimating project budget or team size.

Which standards are used with ISO/IEC 25986:2026?

• ISO/IEC 14143-1:2007 - Clause 1.2 says ISO/IEC 25986:2026 conforms to the mandatory provisions of this functional size measurement foundation standard.
• ISO/IEC TR 14143-5:2004 - Clause 1.3 uses it to define the functional domains where EFS can be applied.
• Nesma ISO/IEC 24570:2018 - Clause 1.2 and Appendix A use it as the high-level FPA reference, and the standard says EFS gives a comparable result.

What does the ISO/IEC 25986:2026 document contain?

ISO/IEC 25986:2026 contains a full method description, practical counting rules and definitions for EFS. Chapter 2 explains the user view, the system boundary, the three component types, the function-point approach and the product/project size distinction.

Chapter 3 gives the counting guidance for common cases such as logical files built from multiple tables, multi-step transactions, output products, help functions, FPA tables, mutation logging and security handling.

Appendix A compares EFS with high-level FPA and reports compatibility research. Appendix B collects the defined terms used throughout the standard.

International
Standard
ISO/IEC 25986
First edition
Software engineering — NESMA
2026-07
functional size measurement
method — Easy functional sizing
(EFS)
Reference number
© ISO/IEC 2026
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© ISO/IEC 2026 – All rights reserved
ii
Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are members
of ISO or IEC participate in the development of International Standards through technical committees
established by the respective organization to deal with particular fields of technical activity. ISO and IEC
technical committees collaborate in fields of mutual interest. Other international organizations, governmental
and non-governmental, in liaison with ISO and IEC, also take part in the work.
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
document should be noted (see www.iso.org/directives or www.iec.ch/members_experts/refdocs).
ISO and IEC draw attention to the possibility that the implementation of this document may involve the use of
(a) patent(s). ISO and IEC take no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO and IEC had not received
notice of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent database
available at www.iso.org/patents and https://patents.iec.ch. ISO and IEC shall not be held responsible for
identifying any or all such patent rights.
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.
In the IEC, see www.iec.ch/understanding-standards.
This document was prepared by NESMA [as EFS v1.0 June 2024] and drafted in accordance with its editorial
rules. It was adopted, under the JTC 1 PAS procedure, by Joint Technical Committee ISO/IEC JTC 1, Information
technology.
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 and www.iec.ch/national-
committees.
© ISO/IEC 2026 – All rights reserved
iii
CONTENTS
1 Scope . 1
1.1 Purpose . 1
1.2 Conformity . 1
1.3 Applicability . 1
1.4 Focus . 1
2 Description of Easy Functional Sizing. 2
2.1 Users and system boundary . 2
2.2 EFS components . 3
2.3 Value EFS components . 5
2.4 Functional size . 5
2.5 Naming convention . 6
3 Practical situations . 7
3.1 Instructions for determining logical files . 7
3.2 Instructions for determining external Inputs and outputs . 8
3.3 Instructions for determining external inputs . 8
3.4 Instructions for determining external outputs . 8
3.5 General support functionality . 9
4 Appendices . 11
Appendix A. Difference high-level FPA and Easy Functional Size . 12
Appendix B. Definitions . 13

© ISO/IEC 2026 – All rights reserved
iv
FOREWORD
The functional size of an automated information system is a determining unit with which, among
other things, reliable estimates for a project budget or team size can be made. Determining the
functional size also plays an important role in newer ways of software development, such as Agile
and DevOps.
Since 2018, the handbook “Definitions and Counting Guidelines for the Application of Function Point
Analysis”, version 2.3 is the starting point for functional size measurement in the Netherlands. In
practice, it appears that the ‘High level function point analysis’ described in this handbook is by far
the most widely used.
Therefore, a strong need has arisen to extract this guideline from the handbook and describe it
separately in order to make this method more accessible. In this process, a further simplification has
been implemented to make it less complex and to cause fewer points of discussion in practice. The
result is the Easy Functional Sizing (EFS) method described in this document. In this simplification,
the most important starting point is that the outcome in function points must be comparable to the
outcome of a high level function point analysis. Research shows that this is indeed the case, see
appendix A.
This International Standard is part of the Nesma publications. The following publications provide
further background and explanation of the counting guidelines. Supporting Nesma publications for
EFS include:
• The handbook Definitions and counting guidelines for the application of function point analysis,
version 2.3.
• Examples illustrating the use of the Nesma FPA method in specific situations and the fully
documented Hotel case.
• The Nesma website nesma.org contains a number of documents that can be used in a specific
context, such as guidelines for the use of FPA in a Data Warehouse environment, with UML
documentation, or for various aspects in contracts.

Intended audience
This standard is for anyone involved in determining the functional size. The intention is that this
standard provides sufficient information for a novice user to perform a size measurement in an
independent and consistent manner.
© ISO/IEC 2026 – All rights reserved
v
STRUCTURE OF THIS STANDARD
After the foreword, Chapter 1 indicates the scope of this standard.
Chapter 2 describes the Easy Functional Sizing (EFS) method. Concepts that form the basis of EFS are
briefly explained.
Chapter 3 provides common practical situations and indicates whether and how these are expressed
in functional size.
Appendix A describes the differences between high level function point analysis and Easy Functional
Sizing. The research shows that there is little difference in outcome.
Finally, appendix B contains the definitions of the concepts used in this International Standard.

© ISO/IEC 2026 – All rights reserved
vi
International Standard ISO/IEC 25986:2026(en)

Software engineering — NESMA functional size measurement
method — Easy functional sizing (EFS)
1 SCOPE
1.1 Purpose
This International Standard specifies the set of definitions, rules and guidelines for applying the
Nesma Easy Functional Sizing method.
1.2 Conformity
This International Standard conforms to all mandatory provisions of ISO/IEC 14143-1:2007. This
International Standard provides a result that is comparable to the result of applying the High-level
FPA of the Nesma-ISO/IEC 24570:2018 standard.
1.3 Applicability
This International Standard can be applied to all functional domains as mentioned in ISO/IEC
TR 14143-5:2004.
1.4 Focus
This International Standard focuses on determining the functional size of an information system in
an easy way. The International Standard does not address aspects that play a role in drawing up a
(project) budget based on this functional size, such as productivity or quality standards. Other metrics
in which the functional size forms a basis are also not discussed.
© ISO/IEC 2026 – All rights reserved
2 DESCRIPTION OF EASY FUNCTIONAL SIZING
EFS is an objective method to determine the functional size of an automated information system (often
called Product in Agile). It's about the what and not the how. The technical solution or the platform
used are irrelevant.
Only those components that are requested by the user and are recognizable and meaningful to the
user are included in the sizing (Functional User Requirement according to ISO 14143-1:2007). These
components are called user functions (Base Functional Components according to ISO 14143-1:2007).
A number of points are assigned to each recognized user function. These points are called function
points. The sum of these function points is the functional size. For example: system XX has a
functional size of 750 function points.
This objectively determined functional size forms the basis for determining the effort and costs of
new build and later functional changes. The functional size is also the basis for a large number of
metrics with which the quality, productivity and output of software development can be determined.
EFS is a compact implementation of the high level function point analysis, as described in Nesma
ISO/IEC 24570:2018 standard and is particularly suitable for quickly and easily determining the
functional size in Agile environments.
2.1 Users and system boundary
EFS is based on the functionality offered to the user by the information system and the information
exchange of the information system with its environment. The functionality is derived from the
incoming and outgoing data flows and the logical data collections that play a role in this information
exchange, data processing and/or data recording.
User and system boundary are important concepts within EFS because they determine the scope and
therefore the functional size. These concepts are further explained here.
2.1.1 Users
EFS recognizes three types of users:
• People and/or organizations that use or are going to use the information system to be
measured, such as end-users, functional administrators, and operators.
• The owner or representative of the owner (often called Product Owner in an Agile
environment) who has requirements (including legal requirements) converted or contributes
(as functionality) to the information system.
• Other information systems that use data or functions of the information system to be
analysed.
Determining the functional size is done from the users' perspective, it is necessary to always perform
such an analysis in cooperation with the users or at least to have verified the result. Only users can
determine which functionality is requested.
© ISO/IEC 2026 – All rights reserved
2.1.2 System boundary
This is the boundary between the information system and its environment (users and or other
information systems). An automated information system is a system for collecting, storing,
processing and presenting data using (software) programs.
Correctly determining the system boundary is important because crossing this boundary determines
whether a data flow should be counted as a user function.
Use the following guidelines when determining the system boundary:
a. Determine who the Product Owner is. If there are multiple Product Owners, there are often
multiple information systems.
b. Use documents that indicate the system boundaries and the system context. Examples include
architecture descriptions (Project Start Architecture), functional design documents, a Class
diagram, or a Context diagram.
c. Consider an information system as a group of programs that are maintained as a whole. The
system boundary encloses this group of programs. All functions within this boundary must be
counted and recorded as a whole.
2.2 EFS components
To determine the functional size, the user functions must be mapped to one of three types of
components. These components determine the amount of functionality of an automated
information system. Chapter 3 describes practical situations, but the breakdown of components are
shown below.
Figure 1 Breakdown of types of user functions
© ISO/IEC 2026 – All rights reserved
2.2.1 Logical File (LF)
A logical file is a logical group of permanent data from the user's perspective that meets at least one
of the following criteria:
• Is used by the information system to be counted and/or
• Is maintained by the information system to be counted.
A logical group of data from the user's perspective is:
a group of data that is considered a meaningful and useful unit or object by an experienced user.
Permanent means:
that the logical file continues to exist after being used by the information system so that it can be
used again.
Used means:
that the data is actually used within the processes of the information system.
Maintained means:
that it is possible to add, modify and/or delete data.
Explanation:
a. Several physical tables in the database can together form one logical file if, from the user's point
of view, they are inextricably linked. For example, consider an Invoice consisting of the Invoice
Header Data and Invoice Lines tables. When the Invoice is deleted, the Invoice Header Data and
also the associated Invoice Lines are automatically deleted. For EFS, these two tables together
form one logical data group.
b. A logical data group that is used can also be part of another information system.
Each recognized logical file counts as 7 function points.
2.2.2 External Input (EI) and External Output (EO)
The following criteria apply to both the External Input and External Output:
a. It is an elementary process, meaning that the function has an autonomous meaning and
performs a complete processing of information. The information system is in a consistent state
after performing the function.
b. Data passes the system boundary of the information system.
c. Unique set of incoming and outgoing data elements and/or unique processing of this data. Set of
data is defined as : the collection of data types requested by the user for an input and output
product, without the aspects that are necessary for the physical implementation. Whether data
is presented on a screen, overview or other medium is not important for EFS.
Subsequently, the primary intent of the user transaction determines which type of user transaction
it concerns: modifying data in the logical files (External Input) or presenting the data (External
Output).
© ISO/IEC 2026 – All rights reserved
External Input (EI)
Any functionality whose primary purpose is to make changes (adding, modifying, and/or deleting data)
in one or more logical files is an External Input.
The external input includes the entire (user) interface: the possible display of data, the business rules,
the actual storage of the data, and the display of an (error) message.
Examples include: adding customer data or deleting product data, but also processing data from
other information systems (for example, in the form of an input file or a message).
An external input can be activated by a user (online), another information system, or automatically
(for example, a batch function that is started in the evening).
Each recognized external input counts as 4 function points.
External Output (EO)
An external output concerns any functionality that presents data to the user or to another system.
This includes the entirety of possibly entering selection data, retrieving the data, calculations, possibly
mutating data, filtering, sorting, presenting the data, and displaying an (error) message.
Examples include: overviews, querying and displaying stored data, data intended for another
information system in the form of files or messages, search functions, and querying item data using
a unique item number.
Each recognized external output counts as 5 function points.
2.3 Value EFS components
The number of function points assigned to each user function can be found in the function point
table
...