Bearing Life Calculator
Rolling bearing L10 life in revolutions and hours from dynamic load rating, equivalent load and speed, with ISO 281 reliability factors and required C.
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About this toolWhat is the Bearing Life Calculator?
A rolling bearing does not wear out on a schedule. Its life is statistical: in a large batch of identical bearings running under the same load, some fail early from rolling contact fatigue and many outlast the average by a wide margin. ISO 281 captures this with the basic rating life L10, the number of revolutions that 90% of the bearings will reach or exceed. This calculator works out L10 in millions of revolutions and in operating hours, then adjusts it for higher reliability with the a1 factors from the standard.
You enter the basic dynamic load rating C from the bearing catalogue, the dynamic equivalent load P (or the radial and axial forces with their X and Y factors) and the shaft speed. The default case, a deep groove ball bearing with C = 14.8 kN carrying 2 kN at 1,500 rpm, gives 405 million revolutions or about 4,500 hours. Ask for 99% reliability and that drops to about 1,130 hours.
Add a target life and the calculator also returns the dynamic load rating you need, so you can go straight to the catalogue for a bearing that fits.
- ISO 281 basic rating life with p = 3 for ball and 10/3 for roller bearings
- Equivalent load entry as P or as Fr, Fa, X and Y
- Reliability factor a1 from 90% to 99.95% using the ISO 281:2007 table, plus a free aISO factor
- Life in revolutions, hours and calendar years, and the C needed for a target life
- Life-at-every-reliability table, formula panel, copy and share link
How to use the Bearing Life Calculator
- Choose ball or roller so the life exponent is 3 or 10/3.
- Enter the basic dynamic load rating C from the manufacturer's catalogue, and choose the force unit you want to work in.
- Enter the dynamic equivalent load P directly, or switch to radial plus axial and enter Fr, Fa and the X and Y factors the catalogue gives for your Fa/Fr ratio.
- Enter the speed in rpm, hours of running per day, a reliability level and, if you have it, an aISO factor and a target life.
- Read L10 in hours and revolutions, the adjusted life, calendar years and the C needed to reach your target. The table shows life at every reliability level.
Worked examples
Small motor bearing
Input
Ball bearing, C = 14.8 kN, P = 2 kN, 1,500 rpm, 90% reliability
Output
L10 = 405.2 million revolutions = 4,502 hours
At 8 hours a day that is about 1.5 years. For 20,000 hours the calculator asks for C = 24.3 kN, so a larger bearing series is needed.
Same bearing at 99% reliability
Input
As above with reliability 99%
Output
a1 = 0.25, L1m = 1,126 hours; C needed for 20,000 h rises to 38.6 kN
Asking for only one failure in a hundred instead of ten in a hundred cuts the usable life to a quarter.
Combined radial and axial load
Input
Fr = 3 kN, Fa = 1.2 kN, X = 0.56, Y = 1.6, C = 14.8 kN, 3,000 rpm
Output
P = 3.6 kN, L10 = 69.5 million revolutions = 386 hours
The axial load adds more to P than its size suggests because Y is larger than X. Check e in the catalogue before using X = 0.56.
Roller bearing on a conveyor pulley
Input
Roller, C = 102 kN, P = 12 kN, 600 rpm
Output
L10 = 1,253 million revolutions = 34,815 hours
Doubling the load to 24 kN drops life to 3,454 hours, a factor of 2^(10/3) ≈ 10.
Background and insight
The rating life equation is L10 = (C/P)^p million revolutions, with p = 3 for ball bearings and p = 10/3 for roller bearings. It grew out of the Lundberg and Palmgren fatigue theory of the 1940s and 1950s and was standardised as ISO 281. Because life varies with the cube of the load ratio, a 10% heavier load cuts ball bearing life by about a quarter, and doubling the load cuts it to one eighth.
ISO 281:2007 introduced a three-parameter Weibull model for reliability. Its a1 factor is 0.95 × (ln(100/R) / ln(100/90))^(2/3) + 0.05, which gives the tabulated values 0.64 at 95%, 0.47 at 97%, 0.25 at 99% and 0.077 at 99.95%. Older catalogues built on the 1990 edition list slightly lower figures such as 0.21 at 99%; the difference matters most above 99% reliability.
The same standard defines a modified life Lnm = a1 × aISO × L10, where aISO accounts for lubricant film thickness, contamination and fatigue load limit. aISO can be well above 1 for clean, well-lubricated bearings and far below it for dirty ones, which is why bearing makers provide their own tools to estimate it. This calculator lets you type aISO in but does not try to derive it.
Common use cases
Selecting a bearing
Work backwards from a target life in hours to the dynamic load rating C you need, then pick a size from the catalogue.
Checking an existing design
See whether a bearing already in a gearbox, pump or fan will meet its service interval at the actual load and speed.
Maintenance planning
Estimate replacement intervals at a reliability level that suits the cost of an unplanned stop.
Comparing ball and roller options
See how much longer a roller bearing lasts at the same load ratio thanks to the 10/3 exponent.
Tips and limitations
- C and P must be in the same unit. The ratio is what matters, so kN, N or lbf all work as long as you do not mix them.
- L10 is a fatigue life under good conditions. Real bearings more often fail from contamination, poor lubrication, misalignment or electrical fluting.
- Very lightly loaded bearings can skid and smear. A common rule of thumb is a minimum load of about 1% of C for ball bearings and 2% for roller bearings; makers give exact figures.
- Use a load spectrum for variable duty: work out the cube-mean equivalent load rather than the peak or the average.
- For slow, oscillating or stationary bearings, check the static rating C0 against the static equivalent load instead.
Frequently asked questions
What does L10 bearing life mean?
L10 is the number of revolutions, or hours at a constant speed, that 90% of a large group of identical bearings will complete before showing the first rolling contact fatigue. Ten percent are expected to fail sooner and about half last roughly five times longer.
How do you calculate bearing life in hours?
Find L10 = (C/P)^p in millions of revolutions, with p = 3 for ball bearings and 10/3 for roller bearings, then convert: L10h = 1,000,000 × L10 / (60 × rpm). A ball bearing with C/P = 7.4 at 1,500 rpm runs about 4,500 hours.
What is the dynamic load rating C of a bearing?
C is the constant radial load (axial for thrust bearings) under which a bearing reaches an L10 life of one million revolutions. It comes from the manufacturer and is calculated to ISO 281, so it can be compared between brands for the same bearing type.
How do I combine radial and axial loads on a bearing?
Use the dynamic equivalent load P = X·Fr + Y·Fa. X and Y come from the catalogue and depend on the bearing type and the ratio Fa/Fr compared with the limit e. When Fa/Fr is at or below e, deep groove ball bearings use X = 1 and Y = 0.
What are the ISO 281 reliability factors a1?
ISO 281:2007 gives a1 = 1 at 90%, 0.64 at 95%, 0.55 at 96%, 0.47 at 97%, 0.37 at 98%, 0.25 at 99%, and down to 0.077 at 99.95%. Multiply L10 by a1 to get the life at the higher reliability.
Why is the exponent 3 for ball bearings and 10/3 for roller bearings?
Ball bearings have point contact and roller bearings line contact, and fatigue tests showed life falls with the cube of load for point contact and with a slightly steeper power for line contact. ISO 281 adopted 3 and 10/3 from the Lundberg and Palmgren work.
How many hours should a bearing last?
SKF's guideline values run from about 300 to 3,000 hours for household appliances and instruments, through 10,000 to 25,000 hours for machines used 8 hours a day, to 40,000 to 50,000 hours for machines running around the clock and 100,000 hours or more for paper machines and similar plant.
Is there an in-depth guide to the Bearing Life Calculator?
Yes. “Bearing L10 Life Explained: ISO 281 Rating Life, Loads and Reliability” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
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