Bearing Life Calculator — L10 and L10h

What the calculation does

The basic rating life follows ISO 281: L10 = (C / P)^p million revolutions, where C is the basic dynamic load rating from the catalogue, P is the equivalent dynamic load your duty produces, and the exponent p is 3 for ball bearings and 10/3 for roller bearings. To express it in hours, multiply by one million and divide by (60 × speed in rpm).

The result is the life reached or exceeded by 90 % of an identical group of bearings under identical conditions. It says nothing about lubrication, contamination or mounting - a bearing with a low L10 but a good film can outlive one with a high L10 in a dirty, starved position.

Worked example

A 20 kN deep groove ball bearing running at 1,500 rpm under a 4 kN equivalent load: C / P = 5 and, with p = 3, L10 = 125 million revolutions, which is 125,000,000 / (60 × 1,500) ≈ 1,389 hours. To reach 20,000 hours at that same duty you need L10 = 20,000 × 60 × 1,500 / 10⁶ = 1,800 million revolutions, so C / P = 1,800^1/3 ≈ 12.2 and C ≈ 12.2 × 4 = 48.7 kN - the calculator returns that figure directly. Life scales with the cube of the load ratio, which is why the rating has to rise so steeply.

Read it as a range, not a promise

Use it to compare candidate bearings and to check that a design has sensible margin - a load ratio C / P below 3 deserves a second look, because real duty rarely stays at the nominal load. For adjusted life, apply the a1 factor for reliability and the aISO factor for lubrication and contamination, or use the load and rating reference for the definitions.