Gearbox Roller Bearing Life Calculator

L10 is the life that 90% of identical bearings reach under the same load and speed before the first sign of fatigue — equivalently, a 10% failure probability. Median life is roughly 5× L10. It is a statistical fatigue life, not a guarantee for any single bearing.

Usually the high-speed input: it turns the most revolutions per unit time, so the same L10 in million revolutions becomes the fewest hours there. The output shaft sees the most load but the fewest revolutions. That is why a 'million revolutions' figure must always be converted to hours at each shaft's own speed — this calculator does that conversion for you.

C (basic dynamic load rating) is printed in every bearing datasheet — for example a 22216 E spherical roller bearing (C = 212 kN) on an intermediate gearbox shaft. P is the equivalent dynamic load: for pure radial load it is simply the radial force; with combined radial + axial load use P = X·Fr + Y·Fa with X and Y from the datasheet.

Because L10 assumes clean lubricant, correct fit and alignment. In practice most bearings die of lubrication failure, contamination, misalignment or fitting damage rather than fatigue. If yours fail early, check the actual load path and the grease before blaming the bearing.

Use p = 3 for ball bearings and p = 10/3 for roller bearings (cylindrical, spherical, taper). Rollers carry load on a line contact rather than a point, so their life is less sensitive to load — that is what the higher exponent encodes.