Bearing Life L10
Compute nominal bearing life L10 in million revs: L10 = (C/P)^p with p=3 (ball) or p=10/3 (roller).
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Bearing L10 life: L10 = (C/P)^p · 10⁶ revolutions
The L10 basic rating life of a rolling bearing tells you how many revolutions 90% of an identical batch will survive before fatigue starts to show. The math is L10 = (C/P)^p · 10⁶ revolutions. Here C is the basic dynamic load rating you read off the manufacturer catalog, P is the equivalent dynamic load actually sitting on the bearing, and the exponent is p = 3 for ball bearings or p = 10/3 for roller bearings (cylindrical, tapered, spherical). Want hours instead of revolutions? Divide: L10h = L10 / (60·n), with n in rpm. Take a deep-groove ball bearing rated C = 12 kN carrying P = 2 kN at 1500 rpm. That works out to L10 = 216·10⁶ revolutions, roughly 2400 hours. The governing standard is ISO 281, and catalogs from SKF, NSK, Timken, FAG and NTN list C, C₀ (static) and the limiting speed for every part number.
Applications
Sizing the bearings on electric motor shafts, gearboxes, pumps and fans. Setting preventive maintenance intervals from the calculated hours of service. Wind turbine main shafts and gearboxes, rail axles, heavy industrial machinery (printing presses, paper mills, mining), HVAC blowers, automotive wheel hubs and transmissions all lean on the same number. The modified lives L10m and Lna go further, folding in lubrication, contamination and reliability factors as ISO 281 lays out.
FAQ
Why "10" in L10? Because about 10% of the bearings are expected to fail by fatigue before they reach that life, which is the same as saying 90% reliability. Want a stricter number? L5 and L1 buy you higher reliability at the cost of a shorter rated life.
Will a real bearing always reach L10? Only if lubrication, alignment and load are all close to ideal. Out in the field, what actually kills a bearing is usually contamination, vibration or misalignment long before fatigue ever gets a chance.
How do I find P? When the load is a mix of radial and axial, fall back on the catalog equivalent-load formula P = X·Fr + Y·Fa. The X and Y coefficients themselves come from the bearing series and the Fa/Fr ratio.
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