Bearing Life Calculator

How Is Bearing Life Calculated?

Bearing life prediction uses the Lundberg-Palmgren equation standardized in ISO 281. L10 life represents the number of revolutions at which 10% of a population of identical bearings will have developed fatigue failure. The remaining 90% will still be operational — it is a statistical reliability metric, not a guaranteed lifetime.

The life exponent p differs by bearing type: p = 3 for ball bearings (point contact) and p = 10/3 for roller bearings (line contact). This means roller bearings are less sensitive to overload than ball bearings. The dynamic load rating C (from the manufacturer's catalog) represents the load that gives exactly 1 million revolutions of L10 life.

Modern bearing life calculations (ISO 281:2007) include the adjusted rating life aISO factor that accounts for lubrication conditions, contamination, and fatigue limit load. With proper lubrication and cleanliness, actual bearing life can be 10-50× the basic L10 calculation. Conversely, poor lubrication or contamination can reduce life to 10% of L10.

Formula: L10 (million rev) = (C/P)^p L10h (hours) = L10 × 10⁶ / (60 × RPM) p = 3 (ball), p = 10/3 (roller) C = Dynamic load rating, P = Equivalent dynamic load

Example Calculation

A 6205 ball bearing (C = 14.8 kN) under 3.5 kN equivalent load at 1500 RPM: L10 = (14.8/3.5)³ = 75.7 million rev. L10h = 75.7 × 10⁶ / (60 × 1500) = 841 hours. For a design target of 20,000 hours, the load must be reduced or a larger bearing selected.

When to Use This Calculator

• Selecting a bearing for a new machine design — verifying that the calculated L10h life meets or exceeds the target design life (typically 20,000-50,000 hours for industrial equipment)
• Evaluating whether a bearing failure was premature — comparing actual service hours against the calculated L10h life
• Comparing different bearing sizes or types for the same application to optimize cost versus reliability
• Determining the maximum allowable load for a bearing to achieve a specified minimum service life

Common Mistakes to Avoid

• Using static load rating (C0) instead of dynamic load rating (C) — the L10 formula requires the dynamic load rating from the bearing catalog
• Ignoring axial loads in the equivalent load calculation — combined radial and axial loads require P = X×Fr + Y×Fa, not P = Fr alone
• Confusing L10 (90% reliability) with median life — 50% of bearings will last approximately 5× the L10 value under the same conditions
• Not accounting for variable loads — using peak load instead of the weighted mean cubic load overestimates required bearing size and cost

How to Interpret Results

• L10h < 5,000 hours: Bearing is undersized for continuous industrial duty — consider a larger bearing or reduced load
• L10h 10,000-30,000 hours: Acceptable for general industrial machinery with normal maintenance schedules
• L10h > 50,000 hours: Bearing is conservatively sized — may be acceptable if space/cost constraints are not critical
• L10h > 100,000 hours: Bearing may be oversized — consider downsizing unless the application demands extreme reliability

Related Standards & References

• ISO 281 — Rolling bearings — Dynamic load ratings and rating life
• ISO 76 — Rolling bearings — Static load ratings
• ISO 15312 — Rolling bearings — Thermal speed rating
• ABMA/ANSI Standard 9 — Load ratings and fatigue life for ball bearings
• ABMA/ANSI Standard 11 — Load ratings and fatigue life for roller bearings

Frequently Asked Questions

Why do bearings often last much longer than the calculated L10 life?

L10 is a conservative, 90th-percentile estimate based on fatigue under ideal conditions. Modern bearing steels (vacuum-degassed, inclusion-free), improved lubricants, and better sealing mean actual median life (L50) is typically 5× the L10 value. With excellent lubrication (κ > 4) and clean conditions, the ISO adjusted life can be 50× the basic L10.

How do I determine the equivalent dynamic load P?

For combined radial (Fr) and axial (Fa) loads: P = X×Fr + Y×Fa, where X and Y are factors from the bearing manufacturer's catalog. For pure radial load, P = Fr. For pure axial load on thrust bearings, P = Fa. If loads vary with time, use the weighted mean cubic load: Pm = ∛(Σ(Fi³×ni)/Σni) where ni is the fraction of time at each load level.

When should I use the adjusted rating life (aISO) instead of basic L10?

Always use the adjusted rating life for design decisions. The basic L10 calculation ignores lubrication quality, contamination, and the bearing fatigue limit. ISO 281:2007 adjustment factor aISO accounts for these real-world conditions: clean oil lubrication with κ > 2 can extend life by 10-50×, while contaminated or poorly lubricated conditions can reduce life to 0.1× L10.