About Bearing Life Calculator
The bearing life calculator estimates the fatigue (rating) life of a rolling-element bearing per ISO 281. It uses the basic dynamic load rating C and the equivalent dynamic load P to compute the basic rating life L10 = (C/P)^p, where the life exponent p is 3 for ball bearings and 10/3 for roller bearings. The result is reported in millions of revolutions and, given a rotational speed, in operating hours.
Enter the equivalent dynamic load P directly, or supply the radial and axial loads with their X and Y factors so the tool computes P = X·Fr + Y·Fa. A reliability factor a1 then scales the basic rating life to other reliabilities — for example a1 = 0.62 for 95 % survival — giving the adjusted life L10a = a1·L10 in both revolutions and hours.
How It Works
- Enter the basic dynamic load rating C (kN) from the bearing catalogue, then either the equivalent dynamic load P directly or the radial load Fr, axial load Fa, and factors X and Y.
- Select the bearing type to set the life exponent p (ball = 3, roller = 10/3) and enter the rotational speed n in rpm.
- The calculator computes the equivalent load P = X·Fr + Y·Fa, the basic rating life L10 = (C/P)^p in Mrev, and the life in hours L10h = (10^6 / (60·n))·L10.
- Choose a reliability (90–99 %) to apply the a1 factor and obtain the adjusted life L10a = a1·L10 in revolutions and hours.
Worked Example
A ball bearing with a basic dynamic load rating C = 30 kN carries an equivalent dynamic load P = 10 kN at n = 1500 rpm. For a ball bearing the life exponent is p = 3, so the basic rating life is L10 = (C/P)^p = (30/10)^3 = 3^3 = 27 million revolutions. Converting to hours, L10h = (10^6 / (60·n))·L10 = (10^6 / (60·1500))·27 = 11.111·27 = 300 hours. At 90 % reliability a1 = 1.0, so the adjusted life equals the basic life; at 95 % reliability a1 = 0.62, giving L10a = 0.62·27 = 16.74 Mrev and L10ah = 0.62·300 = 186 hours.
Formulas
- Equivalent dynamic load
P = X*Fr + Y*Fa- Basic rating life
L10 = (C/P)^p- Rating life in hours
L10h = (10^6 / (60n)) * (C/P)^p- Reliability-adjusted life
L10a = a1 * L10
Standards & References
- ISO 281 (rolling bearing dynamic load ratings and rating life)
- SKF General Catalogue (bearing life calculation)
- ABMA / basic rating life L10
Frequently Asked Questions
What does the L10 rating life mean?
L10 is the basic rating life at 90 % reliability: it is the life, in millions of revolutions, that 90 % of a group of identical bearings is expected to reach or exceed before the first signs of fatigue spalling appear. Equivalently, no more than 10 % of the bearings are expected to fail by that point. It is a statistical fatigue measure, not a guaranteed life for any single bearing.
Why is the life exponent p = 3 for ball bearings but 10/3 for roller bearings?
The exponent reflects how rapidly fatigue life grows as the load drops relative to the dynamic load rating. Ball bearings make point contact and use p = 3, so halving the load multiplies life by 2^3 = 8. Roller bearings make line contact and are less load-sensitive, using p = 10/3 ≈ 3.33, so halving the load multiplies life by about 2^3.33 ≈ 10. These exponents are fixed by ISO 281.
What does the reliability factor a1 do?
The a1 factor scales the basic 90 % rating life L10 to other reliabilities. ISO 281 gives a1 = 1.0 at 90 %, 0.62 at 95 %, 0.53 at 96 %, 0.44 at 97 %, 0.33 at 98 %, and 0.21 at 99 %. A higher required reliability means a lower a1 and therefore a shorter calculated life, because you are asking that a larger fraction of bearings survive.
How do I find the equivalent dynamic load P?
If the bearing carries combined radial and axial load, P = X·Fr + Y·Fa, where X and Y are the radial and axial load factors from the bearing catalogue (they depend on the load ratio and the bearing geometry). For a purely radial load on a radial bearing, P simply equals Fr. You can also enter P directly if it is already known.