ISO/TR 25269:2026

• Abstract:

  This document contains information on the reliability analysis for rolling bearings. The method described only pertains to the fatigue life per ISO 281 or ISO 16281 of rolling bearings. Other mechanisms of failure, like wear, microspalling (gray-staining) or white etching cracks (WEC), lie outside the scope of this document. A multi-row rolling bearing is considered as a single rolling bearing in the context of this document. The method is based on the life analysis per ISO 281 or ISO 16281, thus the general directions and limitations given in these documents apply. The calculated theoretical reliability is not suitable as the only criterion to select or optimize a rolling bearing or rolling bearing arrangements in powertrains, because the actual bearing reliability in service is also dependent on minimum load, rolling element slip, lubricant and lubricant supply, and heat dissipation. The calculated theoretical reliability does not replace or substitute any safety factors used for consideration of uncertainties in load assumptions, e.g. operation factors for shock loads.

• Status: Published
• Publication Date: 25-May-2026
• ICS: 21.100.20 - Rolling bearings
• Technical Committee: ISO/TC 4/SC 8 - Load ratings and life
• Drafting Committee: ISO/TC 4/SC 8/WG 9 - Rolling bearings — Methods for calculating the modified reference rating life for universally loaded bearings
• Current Stage: 6060 - International Standard published
• Start Date: 26-May-2026
• Due Date: 29-May-2027
• Completion Date: 26-May-2026

ISO/TR 25269:2026 is an ISO Technical Report on calculating the theoretical reliability of rolling bearings. It explains how to estimate reliability from fatigue life analysis under ISO 281 or ISO 16281, for engineers and buyers who need to compare bearing life, bearing arrangements, or system reliability in practice. It is a calculation method for fatigue-related reliability, not a general bearing selection rule and not a model for wear, microspalling (gray-staining), white etching cracks (WEC), or other failure modes.

What does ISO/TR 25269:2026 specify?

ISO/TR 25269:2026 specifies a method for reliability analysis of rolling bearings based on fatigue life. It treats a multi-row rolling bearing as a single rolling bearing in this context, and it follows the general directions and limitations of ISO 281 or ISO 16281.

The document is organized into scope, normative references, terms and definitions, symbols, and a calculation clause, with informative annexes for graphs and worked examples.

Annex	What it covers
Annex A	Graphical representation of theoretical reliability and theoretical failure probability
Annex B	Calculation examples for one bearing and for a system of multiple bearings

What are the key requirements of ISO/TR 25269:2026?

ISO/TR 25269:2026 limits the method to fatigue life per ISO 281 or ISO 16281. In practice, that means the calculated reliability should be used for fatigue-based comparisons, not as a substitute for checking other damage mechanisms or application-specific risks.

Clause 5.1 states that rolling bearing fatigue life can be described with either a two-parameter or a three-parameter Weibull distribution. The document also warns that Weibull shape values from the two models are not interchangeable, so the same statistical model should be kept throughout an analysis.

Clause 5.2 says the practical calculation of theoretical reliability is usually based on the modified reference rating life L10mr from ISO 16281. That matters because the calculation can reflect relevant operating parameters of the application instead of relying only on a test result that is difficult or costly to obtain.

Clause 5.2 also defines the reliability calculation in relation to the observation time t. For times up to L10mr, the theoretical reliability is 1, and the same clause gives the relation used to obtain reliability at longer times and the corresponding failure probability Ft. In practice, this gives a direct way to convert life data into a reliability estimate.

Clause 5.3 extends the method to bearing arrangements. The theoretical system reliability is the product of the reliabilities of the individual bearings, which is the relevant approach for systems such as gearboxes or powertrains.

The scope adds an important practical limit: the calculated theoretical reliability is not suitable as the only criterion for selecting or optimizing a bearing or bearing arrangement. Actual service reliability also depends on minimum load, rolling element slip, lubricant and lubricant supply, and heat dissipation, so the calculation still has to be checked against real operating conditions and safety factors for load assumptions.

What terms does ISO/TR 25269:2026 define?

• Theoretical reliability - the probability that a rolling bearing will not fail from the failure modes considered in ISO 281 or ISO 16281 during a stated time or number of revolutions under given operating conditions.
• Theoretical system reliability - the theoretical reliability of an arrangement of multiple individual rolling bearings in a mechanical system.
• B - test life for 10 % failure probability, expressed in million revolutions.
• L10 - basic rating life per ISO 281 for 90 % reliability, expressed in million revolutions.
• L10mr - modified reference rating life per ISO 16281 for 90 % reliability.
• Rt - theoretical reliability at the time of observation t.
• β - shape parameter of the Weibull distribution.
• γ - location parameter of the three-parameter Weibull distribution.
• η - scale parameter of the Weibull distribution.

Who uses ISO/TR 25269:2026?

ISO/TR 25269:2026 is used by bearing engineers, reliability engineers, test engineers, and technical buyers who need a calculated reliability value for rolling bearings. It is also relevant for gearbox, powertrain, and wind energy drivetrain work, where individual bearing reliabilities must be combined into a system value.

Which standards are used with ISO/TR 25269:2026?

ISO/TR 25269:2026 is based on ISO 281:2007 and ISO 16281:2025. ISO 281 provides the basic dynamic load ratings and rating life framework, while ISO 16281 provides the modified reference rating life method for universally loaded rolling bearings.

The introduction also points to ISO/TR 1281-1 and ISO/TR 1281-2:2008 as explanatory notes on rating life and modified rating life calculations. VDMA 23904 and IEC/TS 61400-4-1 are cited as related reliability assessment documents in wind energy and drivetrain applications.

What does the ISO/TR 25269:2026 document contain?

Clause 4 lists the symbols used in the equations, including life values, Weibull parameters, reliability, and failure probability. Clause 5 gives the calculation approach for a single rolling bearing and for a system of bearings, including the relation between reliability and failure probability.

Annex A presents graphs for theoretical reliability and theoretical failure probability. Annex B gives worked examples for one bearing and for a system of two bearings, showing how the formulas are applied in practice for reliability assessment.

Technical
Report
ISO/TR 25269
First edition
Rolling bearings — Calculation of
2026-05
theoretical reliability
Roulements — Calcul de la fiabilité théorique
Reference number
© ISO 2026
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
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or ISO’s member body in the country of the requester.
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 1
5 Theoretical reliability of rolling bearings . 2
5.1 General .2
5.2 Calculation of the theoretical reliability of a rolling bearing .3
5.3 Calculation of the theoretical system reliability .4
Annex A (informative) Graphical representation of theoretical reliability . 5
Annex B (informative) Calculation examples . 6
Bibliography . 7

iii
Foreword
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This document was prepared by Technical Committee ISO/TC 4, Rolling bearings, Subcommittee SC 8, Load
ratings and life.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv
Introduction
The fatigue lives of a population of rolling bearings are subject to a large statistical variation, that is usually
[1]
described by a Weibull distribution. This Weibull distribution also is one fundamental concept in the
statistical accumulation of failure probability used in the analysis of load ratings and rating life of rolling
[2]
bearings per ISO 281 and ISO 16281, see ISO/TR 1281-1 .
However, since rolling contact fatigue life can be described both by a two-parameter as well as a three-
parameter Weibull distribution, different methods have been proposed for the reliability analysis of rolling
bearings.
This document describes a method for the calculation of the theoretical reliability of rolling bearings
[3]
that is consistent with the provisions of both ISO 281 and ISO 16281, as well as VDMA 23904 and
[4]
IEC/TS 61400-4-1 .
v
Technical Report ISO/TR 25269:2026(en)
Rolling bearings — Calculation of theoretical reliability
1 Scope
This document contains information on the reliability analysis for rolling bearings. The method described
only pertains to the fatigue life per ISO 281 or ISO 16281 of rolling bearings. Other mechanisms of failure, like
wear, microspalling (gray-staining) or white etching cracks (WEC), lie outside the scope of this document.
A multi-row rolling bearing is considered as a single rolling bearing in the context of this document.
The method is based on the life analysis per ISO 281 or ISO 16281, thus the general directions and limitations
given in these documents apply.
The calculated theoretical reliability is not suitable as the only criterion to select or optimize a rolling
bearing or rolling bearing arrangements in powertrains, because the actual bearing reliability in service is
also dependent on minimum load, rolling element slip, lubricant and lubricant supply, and heat dissipation.
The calculated theoretical reliability does not replace or substitute any safety factors used for consideration
of uncertainties in load assumptions, e.g. operation factors for shock loads.
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 281:2007, Rolling bearings — Dynamic load ratings and rating life
ISO 16281:2025, Rolling bearings — Methods for calculating the modified reference rating life for universally
loaded rolling bearings
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply. See also the terms and
definitions in ISO 281:2007, Clause 3 and in ISO 16281:2025 Clause 3.
ISO and IEC maintain terminology databases for use in st
...