Drawing No. EH–ME–001 // Mechanical Engineering
Bearing Life Calculator
Reviewed September 2026
Work out how long a rolling-element bearing should last under a given duty — in millions of revolutions and in operating hours — or turn the question round and find the dynamic capacity a target life demands.
Calculation workflow
Inputs are converted internally to SI, the engineering model is solved, and results are converted back to the selected unit system.
Bearing and load
Life results
Life sensitivity to load (same C and speed)
Worked example
A ball bearing with C = 35 kN and P = 6 kN has a basic life of (35/6)³ ≈ 198.5 million revolutions.
For pure radial loading with X = 1 and Y = 0, P = Fr.
L10 = (C/P)^p million revolutions.
Convert revolutions to hours using rotational speed: L10h = 10⁶L10/(60n).
Background
Basic rating life is a statistical rolling-contact fatigue relationship, not a guarantee of service life.
L10 = (C/P)p million revolutions
Use p = 3 for ball bearings and p = 10/3 for roller bearings.
P = XFr + YFa
X and Y must come from the applicable bearing catalog or design standard. Setting X = 1 and Y = 0 is appropriate only when the bearing/load case permits a pure radial equivalent load.
Frequently asked questions
Practical questions about assumptions, limits and interpretation.
L10 is the life that 90% of a large group of identical bearings would reach or exceed under the modelled load and speed, so one in ten is expected to fail earlier. It is a statistical rating, not a guaranteed service life for one specific bearing.
When a bearing carries both radial and axial load, the equivalent dynamic load P is not simply the radial force. X and Y weight the radial and axial components according to bearing type, contact angle and the Fa/Fr ratio. Take them from the manufacturer's catalogue for the exact bearing.
The life exponent p reflects how contact stress scales with load: 3 for ball bearings with point contact, 10/3 for roller bearings with line contact. Because the exponent sits in the power term, it changes the predicted life substantially at the same load ratio.
L10 is quoted at 90% reliability. If the application needs a higher survival probability, a₁ scales the rating life down accordingly — for example about 0.21 at 99% reliability. It adjusts the statistical target only; it does not model lubrication or contamination.
The basic rating life models subsurface fatigue under clean, well-lubricated conditions. Real bearings more often fail from poor lubrication, contamination, misalignment, mounting damage or corrosion. Standards add an a₃ or aᵢₛₒ modifier for those; treat the number here as a fatigue benchmark for comparing options, not a maintenance prediction.
Divide the life in revolutions by the revolutions per hour (rpm × 60). Dividing again by the hours run per day gives the elapsed calendar life, which is usually the figure a maintenance interval is built around.