Process & Mechanical
Bearing L10 Life (ISO 281)
Rolling element bearing rating life from dynamic load rating, equivalent dynamic load, and speed.
Standard method — stated scope limits apply
Enter bearing load rating and operating conditions.
About This Calculation
A rolling-element bearing's rated (L10) life is the number of revolutions (or operating hours) at which 90% of a large population of identical bearings, operating under identical conditions, are still expected to be running — not a guarantee for any single bearing, but a statistically defined design life per ISO 281. Because bearing fatigue life scales with the CUBE (ball bearings) or higher power (roller bearings) of the ratio between dynamic load rating and actual applied load, even a modest overload shortens expected life dramatically, which is exactly why correct load calculation matters far more than it might first appear.
Frequently Asked Questions
Why is L10 defined as 90% survival, not 100%?
Rolling-element fatigue failure is inherently statistical — even identical bearings under identical conditions fail at different times due to microscopic material and manufacturing variation, so no single deterministic "this bearing will last exactly X hours" claim is physically meaningful; L10 is the standard statistical convention across the bearing industry.
Why does doubling the load on a ball bearing cut its life by a factor of 8, not just 2?
Ball bearing fatigue life scales with the load ratio raised to the THIRD power (L10 ∝ (C/P)³) per ISO 281 — this comes from the physics of subsurface fatigue crack initiation under rolling contact stress, and it’s exactly why even modest overloading (from misalignment, unaccounted-for dynamic loads, or incorrect preload) has an outsized effect on real bearing life.
Why do roller bearings use a different life exponent than ball bearings?
Roller bearings have line contact (a rectangular contact patch) rather than a ball bearing’s point contact, which produces a different stress distribution and fatigue behavior — ISO 281 uses an exponent of 10/3 for roller bearings versus 3 for ball bearings to reflect this genuinely different contact mechanics.
Does L10 life account for lubrication and contamination, or only mechanical load?
The basic L10 rating life calculation covers fatigue life under ideal lubrication and cleanliness — modern practice often applies an additional life modification factor (a1a2a3 or the newer ISO 281 aISO factor) to account for actual lubrication condition and contamination level, since poor lubrication or contamination can reduce real bearing life well below the basic calculation.