Bearing Life (L10) Calculator
Calculate L10 bearing fatigue life in hours and million revolutions from dynamic load rating and equivalent load.
Introduction
Rolling bearings do not fail at a fixed lifetime — they fatigue statistically, and the industry's standard yardstick is L10: the life that 90% of identical bearings will meet or exceed under a given load. The Bearing Life Calculator computes L10 in millions of revolutions, hours, and minutes from three catalog and duty-cycle numbers: the dynamic load rating C, the equivalent dynamic load P, and operating speed. It is the ISO 281 basic rating life calculation, the first-pass tool for selecting a bearing, validating an existing design, or estimating a maintenance interval.
How it Works
Basic rating life is L10 = (C ÷ P)^p in millions of revolutions, where the exponent p is 3 for ball bearings and 10/3 for roller bearings — line contact in rollers responds to load differently than point contact in balls. Hours follow from speed: L10h = L10 × 10⁶ ÷ (60 × n). The cubic law makes load dominance vivid: a ball bearing at C/P = 5 lives 125 million revolutions, but doubling load to C/P = 2.5 cuts that to 15.6 million — an eightfold reduction for twice the load.
Usage Scenarios
- Selecting a deep-groove ball bearing for a conveyor pulley: checking that the candidate's C rating delivers at least 40,000 h at the calculated radial load and 500 RPM.
- Explaining a string of premature failures — a misaligned coupling that raised effective load 30% cut theoretical life roughly in half via the cubic exponent.
- Comparing ball versus roller options for a gearbox shaft, where the 10/3 exponent rewards rollers more steeply as C/P margin grows.
- Setting a condition-monitoring interval at a fraction of computed L10 hours so vibration trending starts well before statistical fatigue onset.
- Right-sizing a cost reduction: confirming a smaller bearing still meets the duty cycle after a load reduction in the redesigned assembly.
FAQ
What does L10 actually promise?
That 90% of a population of identical bearings under identical conditions will survive at least that long before fatigue spalling. Median life runs roughly five times L10 — it is a reliability floor, not an average.
Why do rollers use a 10/3 exponent instead of 3?
Empirical fatigue testing shows line-contact stress fields scale differently with load than ball point contacts. ISO 281 codifies p = 3 for balls and p = 10/3 for rollers.
What is equivalent dynamic load P?
A single radial-equivalent load combining your radial and axial components via the bearing's X and Y factors: P = XFr + YFa. For purely radial loading on a deep-groove bearing, P is close to the radial force.
Why might real bearings die before computed L10?
The basic formula assumes clean, well-lubricated, properly mounted bearings at moderate temperature. Contamination, lubricant starvation, misalignment, and vibration all shorten life — adjusted-life methods add correction factors.