ISO/TR 25269:2026

Rolling bearings — Calculation of theoretical reliability

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.

Roulements — Calcul de la fiabilité théorique

General Information

• 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

Overview

ISO/TR 25269:2025, Rolling bearings - Calculation of theoretical reliability provides a standardized method for estimating the theoretical reliability of rolling bearings based on their fatigue life. This technical report, developed by ISO/TC 4/SC 8, aims to support industries worldwide in assessing the expected performance and durability of rolling bearings using statistical methods founded on established ISO standards such as ISO 281 and ISO 16281.

This document is intended for engineers, designers, and maintenance professionals looking to predict bearing reliability in various applications, enabling better-informed decisions in both design and operational contexts. The methodology described focuses specifically on fatigue life – a critical failure mode in rolling bearings – and excludes other mechanisms such as wear or specific metallurgical phenomena.

Key Topics

Statistical Analysis of Bearing Life

• Emphasizes the use of Weibull distributions (two-parameter and three-parameter) to statistically describe rolling bearing fatigue life.
• Sets out parameters and guidance consistent with ISO 281 and ISO 16281 for life and reliability calculations.
• Highlights the difference in shape and location parameters when using two- vs. three-parameter Weibull distributions.

Calculation Methods

• Defines theoretical reliability as the probability a bearing will not fail due to fatigue within a specified period or number of revolutions.
• Presents formulas for calculating the theoretical reliability of a single rolling bearing and systems of bearings.
• Provides symbols and definitions to ensure consistent understanding and usage across industries.

Limitations and Practical Considerations

• Stresses that theoretical reliability calculation should not serve as the sole criterion for bearing selection or system optimization.
• Notes that many real-world variables (e.g., lubrication, heat dissipation, actual load conditions) impact bearing performance beyond what theoretical models can predict.
• Advises that safety factors for uncertainties (such as operation shocks) remain necessary.

Applications

Predictive Maintenance and Asset Management

• Enables maintenance teams and reliability engineers to forecast potential bearing failures and plan preventative interventions.
• Supports lifecycle cost analysis by providing a probabilistic estimate of bearing longevity based on operating conditions and load profiles.

Design and Engineering Optimization

• Helps design engineers compare bearing options and configurations by quantifying reliability under intended use scenarios.
• Facilitates the reliability assessment of complex systems (e.g., gearboxes, powertrains) containing multiple bearings.

Standardized Reporting

• Provides a uniform approach for manufacturers and users to communicate bearing reliability expectations in technical documentation, proposals, and maintenance manuals.

Quality Assurance

• Assists in setting quality benchmarks and performance contracts based on international best practices for rolling bearing reliability prediction.

Related Standards

In addition to ISO/TR 25269, the following standards contribute to the international framework for rolling bearing performance and reliability:

• ISO 281:2007, Rolling bearings - Dynamic load ratings and rating life
  The foundational standard for calculating basic dynamic load ratings and bearing rating life.

• ISO 16281:2025, Rolling bearings - Methods for calculating the modified reference rating life for universally loaded rolling bearings
  Expands on the calculation of rating life by considering specific application parameters.

• ISO/TR 1281-1 and ISO/TR 1281-2, Rolling bearings - Explanatory notes on ISO 281
  Provides background and detailed explanations for interpretations and applications of ISO 281.

• IEC/TS 61400-4-1, Wind energy generation systems - Reliability assessment of drivetrain components in wind turbines
  Addresses reliability modeling for bearings in wind turbine systems, referencing ISO methodologies.

• VDMA 23904, Reliability Assessment for Wind Energy Gearboxes
  Industry-specific guideline for reliability evaluation applicable to wind energy sectors.

Keywords: rolling bearings, theoretical reliability, bearing fatigue life, Weibull distribution, reliability calculation, ISO 25269, ISO 281, ISO 16281, asset management, predictive maintenance, bearing selection, reliability engineering, international standards

Standards Content (Sample)

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
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
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Phone: [phone]
Email: [e-mail]
Website: www.iso.org
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
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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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 document should be noted. This document was drafted in accordance with the editorial rules of the
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ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
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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 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
complete listing of these bodies can be found at www.iso.org/members.html.

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
...