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Basic L10 Bearing Life Calculator - Hours, Revolutions & Reliability-Adjusted Life

Calculate bearing fatigue life from dynamic load rating C and equivalent load P with L10a reliability adjustment

Free bearing life calculator using the ISO 281 L10 formula. Enter the basic dynamic load rating (C) from the bearing catalog, the equivalent dynamic load (P) from your application, and the shaft speed in RPM. The calculator returns bearing life in millions of revolutions, operating hours, and calendar time. The life exponent p is automatically set based on bearing type: 3.0 for ball bearings and 10/3 for roller bearings. L10 life is the number of revolutions at which 90% of identical bearings under the same conditions would still be running. The calculator also shows L10a reliability-adjusted values for 95% (a1 = 0.62) and 99% (a1 = 0.21) survival rates for critical applications where a 10% failure probability is unacceptable. For plant reliability planning, L10a at 95% is the practical design target for equipment that cannot tolerate unplanned downtime. Results include a clear assessment of whether the calculated life meets typical design targets for continuous-duty industrial equipment.

Pro Tip: The L10 formula assumes the load and speed are constant. Real equipment often has variable loads across the duty cycle. If the bearing sees 70% load for 8 hours and 100% load for 2 hours per shift, calculate the equivalent load using the cubic mean formula rather than using the peak load, which will dramatically underestimate bearing life.

Calculate equivalent dynamic load from combined radial and axial forces

Equivalent Dynamic Load Calculator →

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Basic L10 Bearing Life Calculator
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How It Works

  1. Look Up Dynamic Load Rating C

    Find the basic dynamic load rating C from your bearing manufacturer catalog. This is the constant radial load that produces an L10 life of one million revolutions. C is listed in kN or lbf and is specific to each bearing number.

  2. Calculate or Enter Equivalent Load P

    If your bearing has only radial load, P equals the radial load Fr. If both radial and axial loads exist, use the equivalent dynamic load formula or our companion calculator. P must be in the same units as C.

  3. Enter Operating Speed

    Input the shaft speed in RPM. Higher speed means more revolutions per hour, so bearing life in hours decreases even though life in total revolutions stays the same.

  4. Select Bearing Type

    Choose ball bearing (p = 3) or roller bearing (p = 10/3). The life exponent affects how sensitive bearing life is to the C/P ratio. Getting this wrong gives significantly incorrect results.

  5. Review Life Results

    Get L10 life in revolutions, hours, and years. See L10a values at 95% and 99% reliability. Typical industrial design targets are 20,000 to 40,000 hours for continuous duty and 10,000 to 20,000 hours for 8-hour-per-day operation.

Built For

  • Design engineers selecting bearings for new equipment and verifying adequate life expectancy
  • Reliability engineers calculating predicted bearing life for preventive maintenance scheduling
  • Maintenance planners setting bearing replacement intervals based on calculated L10a life
  • Students learning ISO 281 bearing life calculations for mechanical engineering courses
  • Purchasing departments comparing bearing options based on calculated life at the same load and speed

Frequently Asked Questions

L10 is the fatigue life at which 10% of a population of identical bearings will have failed under the same load and speed conditions. In other words, 90% of bearings will last at least this long. It is based on subsurface fatigue spalling, not wear, corrosion, or lubrication failure, which are far more common causes of bearing replacement in practice.
L10 is a statistical prediction for ideal conditions: correct mounting, proper lubrication, no contamination, no misalignment. In practice, contamination, inadequate lubrication, and misalignment cause most bearings to fail well before their calculated L10 life. Conversely, well-maintained bearings in clean, properly lubricated applications often last 3 to 5 times the L10 prediction.
L10 gives 90% reliability. L10a applies a reliability adjustment factor a1 to give higher confidence levels. For 95% reliability, a1 = 0.62 (life is 62% of L10). For 99% reliability, a1 = 0.21 (life is 21% of L10). Critical applications like aviation, medical equipment, or safety-critical machinery typically design to L10a at 99%.
For continuous 24/7 operation, 40,000 hours is a common target. For 8-hour-per-day operation, 20,000 hours is typical. For equipment that is easy to access and repair, 10,000 hours may be acceptable. Equipment in remote or difficult-to-service locations should target 60,000 to 100,000 hours to avoid frequent maintenance trips.
Disclaimer: This calculator uses the basic ISO 281 L10 formula and does not include the aISO life modification factor for lubrication conditions and contamination. For detailed bearing selection, use the manufacturer's bearing selection software (e.g., SKF Bearing Calculator, Timken Syber, NSK Bearing Select) which accounts for lubrication, contamination, and operating conditions.

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