How Bearing Life (L10) Is Calculated
What L10 means, the basic formula, why the C value already includes the material, and a worked example.
What L10 means
No bearing lasts forever — sooner or later, material fatigue causes the surface to start spalling. The L10 life is the number of revolutions that 90% of a group of identical bearings operating under the same conditions can complete without this fatigue damage (i.e. only 10% of the group fail before reaching that number). It expresses a statistical reliability level, not the exact life of a single bearing.
Basic formula
L10 = (C / P)^p
L10 — life in millions of revolutions. C — the bearing's dynamic load capacity (from the manufacturer datasheet, in N). P — the equivalent dynamic load acting on the bearing (in N). p — 3 for ball bearings, 10/3 for roller bearings.
If the rotational speed is known, this value can also be converted to hours:
L10h = (10^6 / (60 × n)) × (C / P)^p
n = rotational speed in revolutions per minute (rpm).
Why the C value already includes the material
C is a value determined by the manufacturer through laboratory testing for that specific bearing (with its particular steel grade, heat treatment, and surface quality) — so the material/quality difference is already embedded inside C. That is why there is no separate "material" input in the calculation; for a correct result you must always take the real C value of your own bearing from the manufacturer's datasheet, as using a generic estimate gives misleading results.
Worked example
C = 25,000 N (from the manufacturer datasheet). P = 5,000 N. Ball bearing (p = 3). L10 = (25,000 / 5,000)³ = 5³ = 125 million revolutions.
Source: ISO 281:2007 — Rolling bearings — Dynamic load ratings and rating life.