Bearing Life Calculator

L10 bearing life formula: L10 = (C ÷ P)^3 million revolutions, where C is dynamic load rating and P is equivalent load — for example, C = 20 kN and P = 5 kN gives L10 = (20÷5)³ = 64 million revolutions. Bearing life is an important factor in the maintenance and reliability of rotating machinery such as motors, pumps, gearboxes, and fans. The L10 life is the industry-standard way to express this: it is the number of revolutions, or operating hours, that 90% of a population of identical bearings will complete or exceed before the first signs of fatigue failure appear. Only 10% of bearings are statistically expected to fail before reaching the L10 life, which is why manufacturers and reliability teams treat it as the baseline figure for planning replacement intervals — it's a conservative, statistical number, not a guarantee for any single bearing.

The calculation depends on two load values: the dynamic load rating C, a fixed value the manufacturer assigns to that specific bearing based on its internal geometry and material, and the equivalent dynamic load P, the actual combined radial and axial load the bearing experiences in service. The ratio of C to P is raised to a power of 3 for ball bearings, or roughly 10/3 for roller bearings, since roller bearings have a different fatigue-load relationship due to their line-contact geometry rather than the point contact of ball bearings.

Continuous-duty estimate. Alongside the raw hours figure, this calculator also converts the life into years assuming the bearing runs continuously (24 hours a day, every day), which is a useful sanity check for planning long-interval maintenance schedules on equipment that runs around the clock, such as process pumps or continuously-running fans.

Formulas Used

Example 1 (ball bearing): C = 25,000 N, P = 5,000 N, speed = 1,450 RPM. Load ratio C/P = 5. L10 = 5³ = 125 million revolutions. Bearing Life = (125 × 1,000,000) ÷ (60 × 1,450) ≈ 1,437 hours, or roughly 60 days of continuous 24/7 running.

Example 2 (roller bearing, same numbers): C = 25,000 N, P = 5,000 N, speed = 1,450 RPM, k = 10/3. L10 = 5^(10/3) ≈ 214.5 million revolutions — nearly double the ball bearing result at the same load ratio, illustrating how the 10/3 exponent produces a higher calculated basic L10 life than the ball-bearing exponent of 3 at the same C/P ratio; actual bearing selection still depends on bearing geometry, load type, speed, lubrication, and manufacturer ratings, not on this exponent alone.

Sensitivity to load — why overloading is expensive

Because life scales with (C/P) raised to the 3rd (or 10/3) power, a seemingly small increase in load produces a large drop in expected life. Doubling the equivalent load P on a ball bearing cuts L10 life to 1/8th of its original value (since 2³ = 8); a 25% overload cuts life to roughly half. This cubic (or near-cubic) relationship is why "just a bit more load than spec" on a bearing is a far bigger reliability risk than intuition suggests, and why correctly calculating P — including any misalignment or shock-load factors — matters more than most other steps in bearing selection.

1. Using the wrong P calculation. Plugging in the radial load alone when there's a meaningful axial component (as in angular contact or tapered roller bearings under thrust) understates P and dramatically overstates the calculated life — always use the manufacturer's X/Y factor combination when axial load is present.

2. Ignoring misalignment. Shaft or housing misalignment concentrates load on one edge of the rolling elements rather than distributing it evenly, effectively raising the real equivalent load far above the theoretical P used in the calculation — this is one of the most common causes of bearings failing well short of their calculated L10 life.

3. Contaminated or wrong-viscosity lubricant. Water ingress, dirt, or metal particles in the lubricant accelerate surface fatigue and can reduce actual life to a small fraction of the calculated value — this is captured by the a23 factor in a full ISO 281 calculation but is invisible in the basic L10 number alone.

4. Treating L10 as a guaranteed replacement interval. L10 is a 90% survival statistic across a population, not a promise for any individual bearing — sound maintenance practice pairs the L10 estimate with condition monitoring (vibration analysis, temperature trending) rather than relying on the calculated hours alone.

5. Ignoring shock and vibration loads. Sudden shock loads — from misaligned couplings, cavitating pumps, or belt-drive shock — impose instantaneous loads far above the steady-state P used in the calculation, and repeated shock loading causes brinelling and premature fatigue that a static load calculation won't predict.