Bearing Life Calculator
L10 life in revolutions and hours from dynamic capacity, load and speed.
Basic rating life to ISO 281. It excludes the life-modification factor for lubrication and contamination, which in a clean, well-lubricated installation multiplies the answer several times over and in a dirty one divides it.
How it works
Rolling bearings do not wear out. They fail by subsurface fatigue — repeated Hertzian contact stress eventually spalls a flake off a raceway — and that is a statistical process, so a bearing does not have a life, it has a distribution of lives.
L10 is the life that 90% of a population exceeds. One bearing in ten is expected to have failed by then, which is not a defect but the definition. The basic equation is
L₁₀ = (C ÷ P)^p × 10⁶ revolutions
with p = 3 for ball bearings and 10/3 for roller bearings.
That exponent is the interesting part. Halving the load on a ball bearing multiplies its expected life by eight. A 20% overload cuts life almost in half. This is why bearing selection is so sensitive to getting the actual load right, and why a machine that runs slightly over its design load does not fail slightly sooner — it fails dramatically sooner.
C ÷ P is the number to look at first. Below about 6 the bearing is heavily loaded and life will be short; above 10 it is comfortable; above 20 it is probably oversized and may suffer from too little load, which lets the rolling elements skid instead of roll and scuffs the raceway.
In practice most bearings never reach their fatigue life. They fail from contamination, from lubricant that broke down or was never there, from misalignment, or from being hammered onto the shaft through the wrong ring. Fatigue life is a ceiling, not a forecast.
Common questions
What are X and Y?
Factors that combine radial and axial load into one equivalent load, and they come from the bearing's own catalogue page because they depend on its internal geometry. For a pure radial load on a deep-groove ball bearing, set X to 1, Y to 0 and axial load to 0.
Is L10 how long it will last?
No. It is the point by which one in ten will have failed from fatigue. The median life is roughly five times L10. Most bearings in the field are removed for something other than fatigue long before either figure.
Why is my bearing failing early?
Contamination and lubrication account for most of it, misalignment for much of the rest. If a bearing fails well inside its calculated life, the calculation is rarely the thing that was wrong.
Can a bearing be too lightly loaded?
Yes. Rolling elements need a minimum load to roll rather than slide, and a lightly loaded high-speed bearing skids and scuffs. Manufacturers publish a minimum load; it is typically 1–2% of C.