Rolling bearings don't wear out at a fixed mileage — they fail by fatigue, and fatigue is statistical. So bearing life is quoted as L10: the life that 90% of identical bearings will reach before the first sign of flaking. It depends on just two loads — the catalogue dynamic load rating C and the equivalent load P the bearing actually sees — raised to a power that rewards margin steeply. Halve the load and a ball bearing lasts eight times longer. This calculator returns L10 in revolutions and converts it to hours at your operating speed.
Reviewed: June 19, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: ISO 281 basic rating life formulation.
The L10 equations
C and P must share the same units (kN is convenient) so their ratio is dimensionless. The exponent is what makes bearing selection forgiving in one direction and punishing in the other: because life goes as the cube (or 3.33 power) of the load ratio, a 25% overload roughly halves the life, while a modest size increase that lifts C can multiply life several-fold.
Worked example — a gearbox shaft bearing
Scenario: A deep-groove ball bearing rated C = 30 kN carries an equivalent load P = 3 kN at 1500 rpm. What is its rating life?
About 11,100 hours, or roughly 1.3 years of non-stop running — comfortably past a typical 8,000–10,000 hour target for intermittent duty. If the load rose to 4 kN, C/P drops to 7.5 and life falls to ~422 million rev (4,700 h), showing how sensitive life is to load. Switching to a roller bearing of the same C/P would extend it further thanks to the 10/3 exponent.
Frequently Asked Questions
The basic rating life: the revolutions (or hours) that 90% of identical bearings reach before fatigue. By definition 10% are expected to have failed at L10.
L10 = (C/P)^p in million revolutions, p = 3 ball / 10/3 roller. Hours: L10h = (10⁶/(60·n))×(C/P)^p with n in rpm.
Exponent differs: p = 3 for ball, 10/3 ≈ 3.33 for roller. Rollers also carry more load per size, so they show longer calculated life for the same C/P.
~5–6 for general machinery, 8–10 for long-life duty, below ~4 life drops fast. Doubling C/P multiplies ball-bearing life by 8.
Guideline L10h: 20,000–30,000 h for shift machines, 40,000–50,000 h for continuous duty, 8,000–12,000 h for intermittent/mobile.