ISO 281 guide

Bearing Life Calculation According to ISO 281

Calculate basic L10 bearing life in revolutions and operating hours, understand the life exponent, and see where modified rating life is needed.

Prepared by BearingSolve8 min readUpdated 13 July 2026

What L10 bearing life means

The basic rating life, commonly written as L₁₀, is the life that 90% of a sufficiently large group of apparently identical bearings is expected to reach or exceed before fatigue develops. It is a statistical rating value, not a guarantee for an individual bearing.

ISO 281 defines the basic relationship between the bearing's basic dynamic load rating C, its equivalent dynamic load P, and rating life.

Basic bearing-life equations

L_{10} = {(\frac{C}{P})}^{p}

million revolutions

L_{10 h} = \frac{10^{6}}{60 n} {(\frac{C}{P})}^{p}

operating hours

Variables in the ISO 281 basic rating-life equation
Symbol	Meaning	Typical unit
`C`	Basic dynamic load rating from the bearing catalogue	kN
`P`	Equivalent dynamic bearing load	kN
`p`	Life exponent: 3 for ball bearings and 10/3 for roller bearings	—
`n`	Rotational speed	r/min

Worked example

Consider a ball bearing with C = 35 kN, P = 10 kN, and n = 1,500 r/min. For a ball bearing, p = 3.

Load ratio: C/P = 35/10 = 3.5
Life in revolutions: L₁₀ = 3.5³ = 42.875 million revolutions
Life in hours: L_10h = 42.875 × 10⁶/(60 × 1,500) ≈ 476 hours

The calculated value describes fatigue rating life under the assumptions of the method. It should not be interpreted as a maintenance interval without considering lubrication, contamination, mounting, temperature, and the application duty cycle.

When basic L10 life is not enough

L_{n m} = a_{1} \times a_{ISO} \times L_{10}

modified rating life

The reliability factor a₁ accounts for a reliability other than 90%. The life modification factor a_ISO incorporates the fatigue load limit, lubrication condition, and contamination level. Use the standard and manufacturer data rather than selecting either factor by intuition.

Common mistake

Speed changes life in hours, but not the basic life expressed in revolutions when C and P remain unchanged.

Standards and further reading

This educational guide does not reproduce the standards. Its equations and examples have been checked against the cited public references, but the guide has not been independently certified or reviewed for your application. Use the current standard, manufacturer data, and an appropriate engineering review for final bearing selection.

Apply the method

Run a complete bearing calculation

Model bearing geometry, loading, lubrication, life, load distribution, and contact stresses in one workflow.

Open BearingSolve