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Bearing Replacement and L10 Life Schedule Worksheet

This editable worksheet calculates basic rating life (L10) in hours for each bearing on your list and compares it to the life you need. Maintenance planners use it to rank which drives deserve attention first and to set replacement or inspection dates.

Download:

L10 (million revs)	L10 life (hours)	Life margin (x required)
756.3347	8,694	0.2173
1,312.1454	121,495	2.0249
326.9246	3,061	0.0765
255.2926	1,467	0.0489
279.5779	14,561	0.2912

Bearings listed

Lowest life margin

0.0489

Shortest L10 life (hours)

1,467

Average life margin

0.5318

Basic rating life per ISO 281: L10 = (C / P)^p million revolutions, and L10h = 10^6 / (60 n) x L10. Example C ratings are typical catalog magnitudes only, so replace them with the values for your exact bearing and series from the manufacturer's catalog. P is the equivalent dynamic load including radial and axial components. A margin below 1 means the bearing is expected to fall short of the required life with 90 percent reliability. Adjusted life with reliability, lubrication and contamination factors (ISO 281 a_ISO) is not included.

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How to use the worksheet

Add one row per bearing position. Enter the catalog dynamic load rating C in kN, the equivalent dynamic load P in kN, the speed and the life you require. Set the exponent to 3 for ball bearings and 3.33 (10/3) for roller bearings. The sheet computes L10 in million revolutions and hours, plus a margin showing how many times the required life you get. Sort by the margin column to find the bearings most at risk and enter a review date for each.

The formula and the standard

Basic rating life under ISO 281 is L10 = (C / P)^p in millions of revolutions, where p is 3 for ball and 10/3 for roller bearings. Dividing by speed gives hours: L10h = 1,000,000 / (60 n) x (C / P)^p. L10 is the life that 90 percent of a group of identical bearings reach or exceed under the stated load. It assumes normal lubrication and no contamination. Modified life with reliability and lubrication factors can be much longer or shorter than the basic value.

Reading the result

A margin of 1 means the basic life exactly equals the target. Margins between about 1 and 2 are tight because actual life varies widely and contamination or misalignment shortens it. Margins above 3 leave room for variation. A fast, lightly loaded motor bearing can show life in the hundreds of thousands of hours and fail early from lubricant aging instead, so use the sheet for load-related wear, not lubrication failures.

Common mistakes

The usual errors are using the static rating C0 instead of the dynamic rating C, mixing kN and N, and using only the radial load when axial thrust applies. Equivalent load P = X Fr + Y Fa needs factors from the bearing catalog. Duty cycles with varying load and speed need a weighted equivalent load, not one nominal point. Treat the worksheet as a ranking tool, then do a full calculation for the critical bearings.

Frequently Asked Questions

What is bearing L10 life?

L10 is the basic rating life: the number of revolutions, or hours at a constant speed, that 90 percent of a large group of identical bearings will reach or exceed before fatigue spalling appears, under a given steady load and normal conditions.

How do I calculate L10 hours?

Divide C by P, raise the result to the power 3 for ball bearings or 10/3 for roller bearings, giving millions of revolutions. Multiply by 1,000,000 and divide by 60 times the speed in rpm to get hours.

Where do I find the dynamic rating C?

It is published in the bearing manufacturer's catalog or online selector for each designation, in kN. Ratings differ by series and brand, so use the value for your exact part. The example values in this sheet are indicative only.

Is a high L10 value a guarantee against failure?

No. L10 covers only fatigue under clean, well-lubricated conditions. Most real bearing failures come from contamination, poor lubrication, misalignment, or installation damage, so combine life calculations with condition monitoring and good lubrication practice.

If you want bearing life, vibration readings and PM work orders in one place, Netray can help connect your maintenance module and condition data.

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