Bearing life calculator
Bearing life is dominated by the load ratio: for a ball bearing, doubling the load cuts the rating life by a factor of eight. This engine computes L10 from the dynamic capacity and equivalent load, converts it to running hours at your speed, and adjusts it for reliabilities above 90%.
| Reliability | a1 | Life (h) |
|---|---|---|
| 90% | 1.00 | 1389 |
| 95% | 0.62 | 861 |
| 96% | 0.53 | 736 |
| 97% | 0.44 | 611 |
| 98% | 0.33 | 458 |
| 99% | 0.21 | 292 |
Life assumes the load and speed stay constant and lubrication is adequate.
L10 = (C/P)^p · p = 3 for ball bearings, 10/3 for roller bearings.
L10h = L10·10⁶/(60n) · Converts revolutions to running hours at constant speed.
Lnm = a1·L10h · a1 = 1 at 90%, 0.21 at 99%.
A clear path from inputs to results.
Bearing life is dominated by one ratio. For a ball bearing, doubling the load cuts the rating life by a factor of eight. This calculator computes the ISO 281 L10 life from the dynamic capacity and equivalent load, converts it to running hours, and adjusts it for reliabilities above 90%.
How to use
- Enter the bearing’s dynamic load rating C from the catalogue.
- Enter the equivalent load P the application actually applies.
- Set the running speed and choose ball or roller.
- Pick the reliability you need and read the adjusted life.
The formula
Reference: ISO 281:2007 rolling bearing rating life; a1 reliability factors.
Worked example
C = 30 kN, P = 6 kN, 1,500 rpm, ball bearing
- Dynamic rating 30 kN.
- Equivalent load 6 kN.
- Speed 1,500 rpm.
- Ball bearing, p = 3.
- 1
Load ratio: 30 / 6 = 5.
- 2
Rating life: 5³ = 125 million revolutions.
- 3
Hours: 125 × 10⁶ / (60 × 1,500) = 1,389 hours.
- 4
At 95% reliability the a1 factor is 0.62, giving 861 hours.
- 5
At 99% reliability the same bearing gives 292 hours.
L10 125 Mrev · 1,389 hours · 861 hours at 95% reliability.
Interpreting the result
The cube is the whole story: a 20% overload costs about 42% of the life, and a 50% overload costs more than two thirds of it. That is why misalignment, belt tension and imbalance matter more than the catalogue rating. Reliability adjustments are equally brutal — moving from 90% to 99% removes almost 80% of the nominal life, which is why critical machinery uses larger bearings than the load alone suggests.
Assumptions & limitations
- Constant load and speed. Variable duty needs a weighted equivalent load and speed.
- Adequate lubrication, clean environment and correct mounting are assumed.
- The basic rating life does not include the ISO 281 life modification factor for contamination and fatigue limit.
- The equivalent load P must already combine radial and axial components using the catalogue X and Y factors.
Frequently asked questions
What does L10 mean?
The life that 90% of a population of identical bearings reaches or exceeds. It is not a guaranteed life for one bearing.
How do I get P?
Combine radial and axial loads with the catalogue factors: P = X·Fr + Y·Fa, adjusted for load and temperature.
Why does a roller bearing last longer?
Its exponent is 10/3 instead of 3, so life falls more slowly as load rises — but the rating itself is usually different too.
Can I use this for a wheel hub or gearbox?
Yes, as a first estimate. Real duty cycles need a weighted load spectrum and often a life modification factor for lubrication.
Methodology last reviewed 2026-10-21. Results are informational and not financial or engineering advice — see our disclaimer.