About the Bearing Life Calculator
This bearing life calculator works out the basic rating life (L10) of a rolling bearing — the number of revolutions, or operating hours at constant speed, that 90% of a large group of identical bearings will reach or exceed before showing the first signs of rolling-contact fatigue. Enter the bearing’s basic dynamic load rating C from the catalogue, the radial and axial loads with their X and Y factors, and the shaft speed.
It is for machine designers choosing between bearing sizes, maintenance engineers estimating replacement intervals and students working through the ISO 281 life equation. You can also pick a higher reliability than 90%, apply an extra life-modification factor for lubrication and contamination (aISO, taken from the bearing maker’s method), and convert the result into calendar years at your duty cycle.
The life equation is statistical: individual bearings vary widely, and half of them will last around five times the L10 life. It assumes correct mounting, adequate lubrication and loads within the bearing’s ratings. With X = 1 and Y = 0 the axial load is ignored; for combined loads, use the X, Y factors from the catalogue for your bearing type and Fa/Fr ratio.
With the default inputs, the basic rating life l10h is 3,811 hours. Change any value above to recalculate instantly.
How to use the bearing life calculator
- 1Choose ball or roller bearing.
- 2Enter the dynamic load rating C from the catalogue, in kN.
- 3Enter the radial and axial loads and the catalogue X and Y factors.
- 4Enter the shaft speed in rpm.
- 5Pick a reliability and, if you have one, an aISO factor.
- 6Read L10h and the modified life in hours and years.
Formula and method
The basic rating life comes from the Lundberg–Palmgren fatigue model standardised in ISO 281. C is the load at which the bearing reaches one million revolutions with 90% reliability, so life scales with the load ratio C/P raised to the exponent p: 3 for ball bearings (point contact) and 10/3 for roller bearings (line contact). Converting to hours divides revolutions by 60 × rpm.
The equivalent dynamic load P combines radial and axial loads using the X and Y factors from the bearing catalogue. For reliabilities above 90%, ISO 281:2007 gives the factor a1 (0.64 at 95%, 0.25 at 99%). The aISO factor, calculated with the maker’s method from lubricant viscosity, temperature, contamination and fatigue load limit, can raise or lower life considerably; leave it at 1 for the basic rating.
- C
- Basic dynamic load rating (kN)
- P
- Equivalent dynamic bearing load (kN)
- p
- Life exponent: 3 for ball, 10/3 for roller bearings
- X, Y
- Radial and axial load factors
- n
- Rotational speed (rpm)
- a1
- Reliability life-modification factor
- aISO
- Systems-approach life-modification factor
Worked examples
Ball bearing, C = 14 kN, 2 kN radial at 1,500 rpm
C/P = 14 ÷ 2 = 7, so L10 = 7³ = 343 million revolutions. At 1,500 rpm that is 343×10⁶ ÷ 90,000 ≈ 3,811 hours — about 1.3 years at 8 hours a day.
Roller bearing with combined load at 99% reliability
P = 0.4 × 8 + 1.6 × 2 = 6.4 kN, so L10 = (60 ÷ 6.4)^(10/3) ≈ 1,737 million revolutions, or about 32,174 hours at 900 rpm. Asking for 99% reliability applies a1 = 0.25, giving about 8,044 hours — under 1.4 years at 16 hours a day.
Small motor bearing at 3,000 rpm, 95% reliability, 24/7
P = 0.56 × 1.5 + 1.8 × 0.6 = 1.92 kN and L10 = (14 ÷ 1.92)³ ≈ 388 million revolutions, or about 2,154 hours at 3,000 rpm. At 95% reliability (a1 = 0.64) the life is about 1,378 hours — under two months of continuous running, so a larger bearing is needed.
Frequently asked questions
What does L10 bearing life mean?+
L10 is the life that 90% of a large group of identical bearings, running under the same conditions, will reach or exceed before fatigue spalling appears. Equivalently, 10% are expected to fail before reaching it.
What is the bearing life formula?+
L10 = (C/P)^p million revolutions, with p = 3 for ball bearings and 10/3 for roller bearings. Convert to hours with L10h = L10 × 1,000,000 ÷ (60 × rpm).
Where do I find the dynamic load rating C?+
The basic dynamic load rating is listed for every bearing in the manufacturer’s catalogue or online product page, usually in kN. It differs between makers and series, so use the figure for the exact part number.
How do I account for axial load?+
Combine loads into an equivalent load P = X·Fr + Y·Fa. The X and Y factors depend on bearing type and on the ratio of axial to radial load; the catalogue gives them along with a limit e below which axial load can be ignored.
How long does a typical bearing need to last?+
Design lives vary by duty: often a few thousand hours for intermittent household equipment, around 20,000–30,000 hours for machines running 8 hours a day, and 40,000–100,000 hours or more for continuously running industrial equipment.