⚙️ Bearing Life (L10) Calculator
Calculate the basic rating life (L10) of rolling bearings based on ISO 281 standards.
Inputs
Results
Bearing Life vs Load Curve
Blue curve: bearing life in hours (L10h) falls as load rises. Red dot: your current operating point — its height equals the L10h result.
Calculator Description
Rolling-element bearings (ball and roller bearings) support a rotating shaft while minimizing friction. Even a perfectly manufactured bearing eventually fails by surface fatigue (spalling) as repeated stress accumulates at the rolling contacts. ISO 281 is the international standard that statistically predicts this fatigue life, and this calculator computes its basic rating life L₁₀.
What this calculator finds: the basic rating life L₁₀
L₁₀ is the life that 90% of a large group of identical bearings will reach or exceed before surface fatigue appears. In other words, only 10% are expected to have failed by that point. It is expressed in millions of revolutions, or in operating hours (L₁₀h) once rotational speed is included. Crucially, it is a conservative life at 90% reliability, not an average life.
Why it matters
- Verifying that a bearing meets a required service life (e.g. 20,000 h) at the design load and speed
- Comparing the dynamic load ratings (C) of candidate bearings to select the best size
- Planning preventive-maintenance intervals, replacement cycles and spares inventory
Formula
ISO 281 Bearing Life Equation
The basic rating life is defined as the ratio of the load rating to the actual load, raised to an exponent. If the rotational speed is known, it is converted into operating hours.
- L₁₀ — Basic rating life (in millions of revolutions)
- L₁₀h — Basic rating life in operating hours [h]
- C — Basic dynamic load rating [N (lbf)] — given in the bearing catalog
- P — Equivalent dynamic bearing load (combined radial/axial load) [N (lbf)]
- p — Life exponent (3 for ball bearings, 10/3 for roller bearings)
- N — Rotational speed [RPM]
How the formula works
- As load P rises, life drops steeply because of the exponent. For a ball bearing (p=3), doubling the load cuts life to one-eighth.
- Choosing a larger bearing with a higher rating C increases the (C/P) ratio and therefore the life.
- A higher speed N reaches the same number of revolutions sooner, so the time-based life L₁₀h becomes shorter.
Worked example
A ball bearing (p=3) with C = 30,000 N runs at an equivalent load P = 3,000 N and N = 1,500 RPM. Then L₁₀ = (30000/3000)³ = 1,000 million revolutions. Converting to hours: L₁₀h = 1,000,000 / (60 × 1500) × 1000 ≈ 11,111 hours.
Useful Tips
Practical tips
- P is the equivalent load, not the pure radial load. If there is axial load, first compute P = X·Fr + Y·Fa (X, Y are bearing-specific factors).
- When longer life is needed, stepping up to a bearing with a higher C is often more effective than reducing load, thanks to the exponent.
- For real reliability, lubrication and contamination, use the modified rating life Lnm = a₁·a_ISO·L₁₀.
Limitations & cautions
- L₁₀ only accounts for surface fatigue. Poor lubrication, contamination, misalignment or overheating cause failures far sooner than predicted.
- For large static (non-rotating) loads, the static safety factor (C₀/P₀) must be checked separately.
- At very low speeds, film formation is difficult and the time-based life may still be short despite a high revolution count.