Bearing L10 Life Calculator (ISO 281)
Basic rating life of a rolling bearing from dynamic load rating C, equivalent load P and speed — L10 in million revolutions and hours for ball (p = 3) and roller (p = 10/3) bearings — with reliability adjustment and the load for a target life.
How it works
L10 (million rev) = (C ÷ P)^p, p = 3 for ball, 10/3 for roller bearings; L10h = L10 × 10⁶ ÷ (60 × rpm); Lₙ = a₁ × L10 (a₁: 0.64 at 95%, 0.25 at 99%)
Rolling bearings fail by fatigue of the raceways, and because fatigue is statistical the standard measure is the life that 90% of a batch will reach — the L10 life. ISO 281 relates it to the ratio of the catalogue dynamic load rating C (the load for exactly one million revolutions) to the actual equivalent load: life falls with the cube of load for ball bearings and the 10/3 power for rollers, so doubling the load cuts life by eight times. Converting to hours needs the speed. Reliability factors scale the result for applications that cannot tolerate a 10% failure rate, and the modern “modified life” multiplies by a lubrication-and-contamination factor that can swing the answer by an order of magnitude in either direction — a clean, well-oiled, lightly loaded bearing can far outlive its L10.
Worked example
A 6210 deep-groove ball bearing (C = 35.1 kN) under 4.5 kN at 1,450 rpm: (35.1/4.5)³ = 475 million revolutions ≈ 5,460 hours L10 — short; for 20,000 h the load would need to drop to about 2.9 kN or a larger bearing chosen.
Frequently asked questions
What is the equivalent load P?
A single radial load that would give the same life as the combined radial and axial loads: P = X·Fr + Y·Fa with X and Y from the bearing catalogue (for deep-groove ball bearings Y depends on Fa/C₀).
Why does my bearing fail long before L10?
Usually not fatigue: contamination, wrong or degraded lubricant, misalignment, excessive preload or fitting damage. Only about a third of bearing failures are true fatigue.
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Engineering estimate for education and preliminary design. Use manufacturer data, applicable standards and appropriate safety factors, and have critical designs checked by a qualified engineer.