Bearing Life Calculator

Calculate L10 basic and adjusted rating life per ISO 281. Determine expected service hours from catalog load ratings and operating conditions.

Input Parameters

1.0 = normal conditions, 0.1–0.5 = contaminated, up to 50 for optimal conditions

Results

Enter bearing parameters and click Calculate.

Reverse Calculation

Find the minimum dynamic load rating (C) needed to achieve a target service life.

Understanding Bearing Life Ratings

The L10 rating life is the number of revolutions (or hours at a given speed) that 90% of a group of identical bearings will reach or exceed before the first sign of fatigue appears. Put another way, there is a 10% probability that any individual bearing will fail before reaching its L10 life. This is a statistical measure defined by the ISO 281 standard, not a guarantee of any single bearing's service life.

The adjusted rating life L10a applies two modification factors to the basic L10 value. The reliability factor a1 adjusts for survival probabilities higher than 90%, and the life modification factor aISO accounts for real-world operating conditions including lubrication film thickness, contamination levels, and load distribution within the bearing.

The Life Exponent

Ball bearings use a life exponent of p = 3, while roller bearings use p = 10/3 (approximately 3.33). This difference arises from the contact geometry: ball bearings make point contact with the raceways, producing a Hertzian contact ellipse, while roller bearings make line contact along a rectangular patch. The resulting differences in subsurface stress distribution and fatigue crack propagation rates are what drive the different exponent values. These exponents were established empirically by Lundberg and Palmgren in the 1940s and remain codified in ISO 281.

Factors Affecting Real-World Life

  • Lubrication: Adequate lubrication film thickness is the single most important factor. A proper elastohydrodynamic film prevents metal-to-metal contact between rolling elements and raceways. Insufficient lubrication can reduce actual life to a fraction of the calculated value.
  • Contamination: Solid particles in the lubricant cause surface denting and stress concentrations that accelerate fatigue. Even particles smaller than the lubricant film thickness cause damage. The aISO factor can drop below 0.5 in heavily contaminated environments.
  • Alignment: Misalignment between the shaft and housing creates uneven load distribution across the rolling elements, increasing the maximum contact stress. Angular misalignment beyond the bearing's tolerance significantly reduces life.
  • Temperature: Elevated operating temperatures reduce lubricant viscosity, thin the elastohydrodynamic film, and can degrade the lubricant itself. Bearing materials also lose hardness at sustained temperatures above 120°C (250°F), directly reducing fatigue resistance.
  • Mounting and fit: Incorrect interference fits, improper preload, or poor surface finish on the shaft and housing bore all influence the internal load distribution and can lead to premature failure.

Calculated bearing life is a statistical prediction based on idealized conditions. Actual service life varies widely depending on installation quality, operating environment, and maintenance practices. For critical equipment, continuous condition monitoring provides direct evidence of bearing health rather than relying solely on calculated life predictions. Learn more about bearing monitoring approaches at iotbearings.com.