Bearing Life Calculator

L10 Bearing Life Concept

The L10 life represents the number of revolutions (or hours at a given speed) that 90% of a group of identical bearings will complete or exceed before the first evidence of fatigue develops. In other words, 10% of bearings may fail before reaching L10 life.

Basic Rating Life Formula (ISO 281)

The basic rating life in millions of revolutions is:

L10 = (C/P)^p x 10^6 revolutions

Where:

• C = Basic dynamic load rating (from manufacturer)
• P = Equivalent dynamic bearing load
• p = Life exponent: 3 for ball bearings, 10/3 for roller bearings

Converting to operating hours:

L10h = (10^6 / 60n) x (C/P)^p hours

Dynamic vs Static Load Ratings

• C (Dynamic): The constant load that gives L10 = 1 million revolutions. Used for rotating bearings.
• C0 (Static): Maximum load before permanent deformation occurs. Used for stationary or slow rotation (<10 RPM).

Adjusted Life (Lna)

ISO 281 provides modification factors to adjust the basic rating life:

Lna = a1 x a2 x a3 x L10

• a1 - Reliability factor (reduces life for higher reliability requirements)
• a2 - Material factor (bearing steel quality)
• a3 - Operating conditions factor (lubrication, contamination)

Equivalent Dynamic Load (P)

For combined radial (Fr) and axial (Fa) loads on ball bearings:

P = X x Fr + Y x Fa

Where X and Y are factors depending on the Fa/(Fr) ratio and bearing geometry. For deep groove ball bearings with Fa/Fr ≤ e: X=1, Y=0. For Fa/Fr > e: X=0.56, Y varies from 1.0 to 2.3 based on Fa/C0.