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How to Determine Approximate Bearing Life

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When selecting a bearing for an application, it is often helpful to know what the expected life will be. The standard industry measurement is L10 bearing life. This is the number of hours at a constant speed that a group of bearings will reach before 10% of bearings fail.

Keep in mind that designed life and actual life will be different. Designed life calculations will never account for all the variables life throws at an application. The L10 calculation assumes ideal operating conditions, and we know those are few and far between. Some studies show that approximately 10% of bearings reach their calculated lifespan, though there are innumerable reasons for this.

The formula and table below will provide a few critical pieces of information for your bearing application. It will provide you with the required capacity of the bearing and the maximum radial load you can impose.

If you know your bearing’s dynamic capacity, imposed radial load, and RPM, you can calculate your own L10 bearing life. This gives you an idea as to how long you can expect your bearing to run.

L10 Calculation

If you need to know what the bearing capacity needs to be for your application and have the imposed radial load, RPM, and an idea of how long the bearing needs to last, the table below can provide you with that answer. A simplified L10 life chart is found below, but neither includes every viable application or L10 life.

Example: A 100lb fan running at 1200RPM requires a 40,000 hour life. The Cr/P factor is 14.2. Multiplying that factor by the weight of the fan (14.2×100) will provide you the minimum required capacity of the bearing, in this case 1,402lbs. A bearing with a capacity larger than this will provide you with the 40,000 hours required.


Calculations like those above may seem difficult, but they provide valuable information that relates directly to the life of a bearing.

By running through these calculations and tables you’re providing yourself with both the amount of hours you can expect your bearing to run and also how safely under the allowable radial load your application is.

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