How to use the Bearing L10 Life Calculator
- 1. Pick the jobFind the life of a bearing, or the C rating you need.
- 2. Enter loadsRadial and axial load, X and Y factors and the service factor.
- 3. Read the lifeEquivalent load, L10, life in hours and the life at your reliability.
Bearing life formulas
The basic rating life (90% reliability) is L10 = (C/P)^p million revolutions, with p = 3 for ball bearings and p = 10/3 for roller bearings.
- Equivalent dynamic load P = Ka (X·Fr + Y·Fa). With no axial load, or Fa/Fr ≤ e, X = 1 and Y = 0.
- Life in hours: L10h = L10 × 10⁶ / (60N).
- Other reliabilities: L = a1 × L10, with a1 = 0.64 at 95% and 0.25 at 99% (ISO 281).
- Rating needed: C = P × L^(1/p), where L = 60 N Lh / 10⁶.
C, X, Y and e come from the manufacturer's catalogue or the data book used in your course.
Worked example and exam tips
A ball bearing with C = 35 kN carries a radial load of 5 kN at 1000 rpm. L10 = (35/5)³ = 343 million revolutions, which is 343 × 10⁶ / 60 000 = 5717 hours. For 20 000 hours at the same speed and load, the bearing needs C = 5 × 1200^(1/3) = 53.1 kN.
- Doubling the load cuts a ball bearing's life to one-eighth.
- Apply the load or service factor before raising to the power p.
- Older textbooks use a1 values of 0.62 (95%) and 0.21 (99%). Pick "Other a1" to use them.
Frequently asked questions
What does L10 mean?
It is the life that 90% of a group of identical bearings will reach or exceed before the first sign of fatigue.
Where do I get C, X and Y?
From the bearing catalogue (SKF, FAG, NBC) or the design data book. The default numbers here are examples only.
Why is the exponent 10/3 for roller bearings?
Rollers make line contact rather than point contact, and tests show the life follows (C/P) to the power 10/3.
Is this calculator free?
Yes. You fill in a short form once to see your result, and the other Uncodemy tools then open without it. Every calculation runs in your browser and nothing you type is sent anywhere.