Bearing Life Calculator
Calculate L10 bearing life in revolutions and hours using the ISO 281 basic rating life equation for ball and roller bearings.
About this calculator
Bearing life is a probability statement, not a fixed number: L10 life is the number of revolutions (or hours) at which 90% of a batch of identical bearings, run under identical conditions, are expected to still be operating without fatigue failure. This calculator applies the ISO 281:2007 basic rating life equation (Rolling bearings — Dynamic load ratings and rating life), L10 = (Dynamic Load Rating / Equivalent Dynamic Load) raised to the Load-Life Exponent, times one million revolutions. The exponent depends on the bearing's internal geometry -- p = 3 for ball bearings, whose contact is a point, versus p = 10/3 for roller bearings, whose contact is a line. Converting revolutions to L10 Life (Hours) divides by 60 x Operating Speed, since a bearing spinning faster burns through its total revolution budget in less wall-clock time even though it hasn't done any more "damage" per revolution.
Because the load ratio is raised to a power of 3 or higher, the Equivalent Dynamic Load has an outsized effect on predicted life: modest increases in operating load translate into large drops in expected service hours. The Adjusted L10 Life applies the ISO/TR 1281-2 reliability modification factor a1 for whichever Reliability you select (a1 = 1.0 at the default 90%, falling to 0.21 at 99%), on top of an assumed life modification factor of 1.0 for clean conditions and proper lubrication -- so at the 90% default it equals L10 Life exactly, and only diverges once you select a higher reliability. The L5 Life (95% Reliability) output shows the shorter, more conservative life expected if only 5% of bearings are allowed to fail rather than 10% -- useful when a single bearing failure is costly or safety-critical.
Inputs
Results
L10 Life (Hours)
1,157 hrs
Adjusted L10 Life
1,157 hrs
Figures current as of 2007. Source: International Organization for Standardization, ISO 281:2007, Rolling bearings — Dynamic load ratings and rating life
How to Use This Calculator
- Enter the Dynamic Load Rating (C) in lb from the bearing manufacturer's catalog — this is the load at which 90% of bearings survive 1 million revolutions.
- Enter the Equivalent Dynamic Load (P) in lb, combining radial and axial forces using P = XFr + YFa from the catalog X and Y factors.
- Set the Operating Speed in RPM. Common motor-driven speeds are 1200, 1750, and 3600 RPM.
- Select the Load-Life Exponent: p = 3 for ball bearings, p = 10/3 for roller bearings.
- Select the Reliability you need. 90% (the default) makes Adjusted L10 Life equal L10 Life; higher reliability values apply the ISO/TR 1281-2 a1 factor to shorten it.
- Review the L10 Life in hours — this is the service life at which 10% of bearings are expected to fail. The Adjusted L10 Life applies your selected reliability factor on top of it.
- Compare the L5 Life (95% reliability) if higher confidence is required for critical machinery.
How the result changes with Equivalent Dynamic Load (P)
| Equivalent Dynamic Load (P) | L10 Life (Hours) | Adjusted L10 Life |
|---|---|---|
| 1,000 | 9,259 hrs | 9,259 hrs |
| 1,500 | 2,743 hrs | 2,743 hrs |
| 3,000 | 343 hrs | 343 hrs |
| 5,000 | 74 hrs | 74 hrs |
What each input means
- Dynamic Load Rating (C)
- Basic dynamic load rating from the bearing catalog. The load at which 90% of bearings survive 1 million revolutions.
- Equivalent Dynamic Load (P)
- Equivalent dynamic bearing load combining radial and axial forces. P = XFr + YFa (from bearing catalog).
- Operating Speed
- Rotational speed of the bearing. Must be within the bearing's speed rating.
- Load-Life Exponent (p)
- Life exponent depends on bearing type. Ball bearings use p=3; roller bearings use p=10/3.
- Reliability
- Required reliability for the Adjusted L10 Life, per the ISO/TR 1281-2 a1 factor. 90% (the L10 default) applies no adjustment.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersDynamic Load Rating (C) = 10000, Equivalent Dynamic Load (P) = 2000, Operating Speed = 1800, Load-Life Exponent (p) = 3 = 4 input(s) provided
- Calculate L10 LifeL10 Life1157 = 1157
- Calculate Adjusted L10 LifeAdjusted L10 Life1157 = 1157
- Calculate L10 LifeL10 Life125000000 = 125000000
- Calculate L5 LifeL5 Life718 = 718
Figures and sources
- L10 basic rating life equation and reliability modification factor a1 (2007) — International Organization for Standardization, ISO 281:2007, Rolling bearings — Dynamic load ratings and rating life
Engine last updated . Checked against 1 independently-derived test — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does a small increase in load cause such a large drop in bearing life?
L10 life is calculated as (Dynamic Load Rating / Equivalent Dynamic Load) raised to the Load-Life Exponent (p = 3 for ball bearings, p = 10/3 for roller bearings), then multiplied by one million revolutions. Because the load ratio is raised to a power of 3 or more, a modest increase in Equivalent Dynamic Load produces a disproportionately large drop in predicted life -- doubling the load can cut expected life by a factor of 8 or more for ball bearings.
Does running a bearing faster shorten its L10 Life in hours?
Yes. The L10 Life in revolutions depends only on the load ratio and stays the same regardless of speed, but converting to hours divides by Operating Speed (L10 Hours = L10 Revolutions / (60 x RPM)). A bearing spinning at 3,600 RPM burns through the same total revolution budget in half the wall-clock time of one spinning at 1,800 RPM, so higher operating speed always means fewer service hours even though the bearing itself isn't wearing out any faster per revolution.
What's the practical difference between L10 Life and L5 Life (95% Reliability)?
L10 Life is the life at which 90% of bearings in a batch are still running -- a 10% expected failure rate. L5 Life (95% Reliability) is the more conservative figure at which only 5% are expected to have failed, calculated here by applying a 0.62 reliability factor to the L10 hours. Use L5 for critical applications where a single bearing failure is costly or dangerous, and L10 for routine industrial equipment where scheduled replacement is acceptable.
Why do ball bearings and roller bearings use different exponents?
Ball bearings make point contact with the raceway, while roller bearings make line contact along the roller's length. That geometric difference changes how stress concentrates under load, which is why ISO 281 assigns ball bearings a Load-Life Exponent of p = 3 and roller bearings p = 10/3 (about 3.33) -- a higher exponent that makes roller bearing life slightly less sensitive to load ratio changes than ball bearing life.
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