How to use this calculator
- Enter the dynamic load rating. Enter the basic dynamic load rating C from the bearing catalogue.
- Enter the equivalent load. Enter the equivalent dynamic load P on the bearing.
- Enter the speed. Enter the operating speed in RPM.
- Pick the bearing type. Choose ball (p = 3) or roller (p = 10/3).
- Read the life. Read the L10 life in million revolutions and in hours, plus the C/P ratio.
How it works
The ISO 281 basic rating life is
L₁₀ = (C / P)^p
in million revolutions, where C is the basic dynamic load rating from
the catalogue, P the equivalent dynamic load, and the load–life
exponent p is 3 for ball bearings and 10/3
for roller bearings. Because of the cube law (ball bearings), the life is very
sensitive to load: halving the load multiplies the life by about 2³ = 8.
Convert to a life in hours with the speed:
L₁₀ₕ = 10⁶ / (60 · n) × (C / P)^p, where n is the speed in
RPM. L₁₀ is a 90%-reliability rating — the life that 9 of 10 bearings reach.
Worked example
Verified against the live calculator
A ball bearing with a dynamic load rating C = 30 kN under an equivalent
load P = 5 kN at 1,500 RPM: the ratio is C/P = 6, so
L₁₀ = 6³ = 216 million revolutions. In hours that is
216 × 10⁶ / (60 × 1500) ≈ 2,400 hours. The calculator returns exactly
this — and switching to a roller bearing raises L₁₀ to 6^(10/3) ≈ 392
million revolutions.
Frequently asked questions
How do you calculate bearing life (L10)?
Use the ISO 281 basic rating life L10 = (C/P)^p in million revolutions, where C is the basic dynamic load rating, P the equivalent dynamic load, and p the load–life exponent (3 for ball bearings, 10/3 for roller bearings). For a life in hours, L10h = 10⁶ / (60·n) × (C/P)^p, with n the speed in RPM.
What is L10 (or B10) life?
L10 — also written B10 — is the basic rating life that 90% of a group of identical bearings will reach or exceed under a given load and speed. Put the other way, up to 10% may fail by that point. It is a statistical rating at 90% reliability, not a guaranteed minimum for any single bearing.
What is the load–life exponent for ball vs roller bearings?
The exponent p in L10 = (C/P)^p is 3 for ball bearings and 10/3 (≈ 3.33) for roller bearings. Roller bearings make more contact area, so their life rises slightly faster as the load ratio C/P increases.
How do I convert bearing life from revolutions to hours?
Divide the million-revolution life by the revolutions per hour: L10h = L10 × 10⁶ / (60·n), where n is the speed in RPM. For example 216 million revolutions at 1,500 RPM is 216 × 10⁶ / (60 × 1500) = 2,400 hours.
What is the basic dynamic load rating C?
C is the constant radial (or axial) load a bearing can theoretically carry for a basic rating life of one million revolutions. It is a catalogue value published by the bearing manufacturer for each part number — read it straight from the datasheet and enter it as C.
Does doubling the load halve the bearing life?
No — life drops far faster than that. Because life goes with the cube of the load ratio (ball bearings), doubling the equivalent load P cuts the L10 life to about one-eighth (2³ = 8), not one-half. For roller bearings the factor is 2^(10/3) ≈ 10.
Method & assumptions
- Basic rating life L₁₀ at 90% reliability (per ISO 281) — 10% of bearings may fail before it.
- Ignores lubrication, temperature, contamination and the a₁ / a₂₃ / aISO modification factors of the modified rating life.
- P is the equivalent dynamic load — combine the radial and axial loads separately (P = X·Fr + Y·Fa) before entering it.