Bearing Life Estimator Calculator
Estimate bearing L10 life based on load, speed, and bearing ratings. Understand how bearing life is calculated, the role of lubrication, and when to schedule replacements.
Inputs
From bearing manufacturer's catalogue
Radial + axial load combined
Results
244,140,625 rev
2,713 hours
≈ 0 years continuous operation
6.25
Higher ratio = longer life
How L10 Life is Calculated
L10 life is the operating life that 90% of a group of identical bearings will exceed under identical load and speed conditions. It is the standard bearing life metric defined by ISO 281.
Where: C = basic dynamic load rating (N), P = equivalent dynamic load (N), p = 3 for ball bearings, p = 10/3 for roller bearings
Where: n = rotational speed (RPM)
Understanding the Exponent (p)
The exponent p differs between ball and roller bearings because of how the rolling elements distribute contact stress:
- Ball bearings (p = 3): Point contact between ball and raceway. Stress is concentrated, so life is more sensitive to load changes.
- Roller bearings (p = 10/3 ≈ 3.33): Line contact between roller and raceway. Stress is distributed over a larger area, so life is slightly less sensitive to load changes.
Key insight: Because life is proportional to (C/P)^3, doubling the load reduces bearing life by a factor of 8 (2³ = 8). This is why bearing selection should always include a generous safety margin on load capacity.
Adjusted Bearing Life (a1, a2, a3)
The basic L10 life can be adjusted to account for reliability, material, and operating conditions:
- a1 (reliability): 1.0 for 90% reliability (L10), 0.62 for 95% (L5), 0.37 for 97% (L3), 0.25 for 98% (L2)
- a2 (material): 1.0 for standard steel, 3.0+ for vacuum-degassed or ceramic hybrid bearings
- a3 (operating conditions): Depends on lubrication viscosity, cleanliness (filtration), and temperature. Poor lubrication or contamination can reduce a3 to below 0.1.
When to Schedule Replacement
- Design life target: Most industrial bearings are selected for an L10h of 50,000–100,000 hours (5–11 years continuous operation).
- Condition-based replacement: Monitor vibration (envelope/demodulation), temperature, and oil condition. Replace when trends show early bearing wear — do not wait for failure.
- Consider lubrication: Grease-lubricated bearings should be re-lubricated at intervals of 0.5–1× the grease life. Oil-bath bearings should have oil changed annually.
- Contamination control: Even a small amount of contaminant (10 μm particles) can reduce bearing life by 50%+. Use appropriate seals and filtration.