What is L10 Life?

Bearings are a simple, but integral component in any industrial application. The premature failure of a bearing can mean costly unplanned downtime that could have been prevented using the proper predictive measures. When specifying the average lifespan of a bearing, I suggest using the American Bearing Manufacturers Association’s (ABMA) preferred method, calculating for L10 life.

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In the simplest terms, L10 life is calculating, with 90% reliability, how many hours a bearing will last under a given load and speed. There is a 10% probability that at the applied load and speed, 10% of a population of identical bearings would suffer a fatigue failure, typically pitting on the raceway of the bearing.. Note that this does not address failures caused by other conditions such as contamination, wear, misalignment, and improper lubrication. Average life, sometimes called Mean Time Between Failure (MTBF), is about five times the calculated L10 life. If there is a significant difference in bearing lives between drives, a different reliability basis may have been used. Another cause of bearing life differences is the use of adjusted, or advanced, life calculation procedures based on ISO 281 or a bearing manufacturer’s in-house calculation methods. These methods take into account oil viscosity, oil temperature and the contamination level in the oil during service. To achieve these calculated lives, it requires the end user to maintain oil quality and contamination to a specified level. This may require continuous oil filtration or frequent oil changes with new filtered oil to maintain the conditions specified by the calculations. When bearing life is quoted, it is important to understand what assumptions are made to arrive at that value.

The equation for L10 Life

The equation for L10 life can be seen above, where speed is the shaft speed in RPM, Dynamic Capacity is the C value obtained from bearing manufactures catalogs, Equivalent radial load is the applied load that the bearing sees as a function of actual radial and axial loading as well as bearing geometry. For an advanced L10 bearing life calculation, multiply the result by aISO. By completing this equation, you should be able to calculate, with relative certainty, how many hours 10% of bearings will have failed under the calculated load. As the equation is theoretical, it cannot account for variables such as improper installation and maintenance, but it is a good way to determine an expected lifespan based on your specific application.

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Understanding Your Gear Drive Ratings Whitepaper

To learn more about Miner’s Rule and Gear Drive ratings in general, download my whitepaper, Understanding Your Gear Drive Ratings.


Frank C   Uherek

Frank has been a Principal Engineer for the Rexnord Gear Group for over 10 years. Before his tenure at Rexnord, he spent time at Regal Beloit, Flender Corporation and Winergy Drive Systems Corporation. In addition to his responsibilities at Rexnord, Frank is an active committee chair on both AGMA and ISO rating committees. Frank holds a Bachelor of Science in Mechanical Engineering and a Masters of Business Administration in Production and Accounting from the Illinois Institute of Technology.