Enter the basic dynamic load rating C from the bearing's datasheet, the equivalent dynamic load P on it, and the shaft speed — this returns the ISO 281 basic rating life in million revolutions, operating hours and years, using the correct life exponent for ball or roller bearings and the published a1 factor for reliabilities above 90%. Everything here is the standard formula; nothing is looked up from a table of our own.
Rating life
million revolutions
Rating life
operating hours
Continuous running
years at 24/7
Read this before you use the number. Basic rating life assumes adequate lubrication, clean operating conditions, correct mounting and alignment, and that the load you entered is the true operating load. It models rolling-contact fatigue only. Most bearings removed from service in the field never reach that fatigue limit — they are lost to lubrication problems, contamination, misalignment or mounting damage first. Use this to compare candidate bearings under identical assumptions; do not use it as a maintenance interval on its own.
The formula this uses
ISO 281 defines the basic rating life as
L10 = (C / P)p million revolutions
and, converted to operating hours at a constant speed n in RPM,
L10h = (106 / 60n) × (C / P)p hours
where C is the basic dynamic load rating published by the manufacturer for that specific bearing, P is the equivalent dynamic bearing load derived from the actual radial and axial loads, and p is the life exponent: 3 for ball bearings, 10/3 for roller bearings.
Selecting a reliability above the default 90% multiplies the result by the ISO 281 a1 factor. Because life varies with the cube of the load ratio, small load reductions buy large life increases — halving P multiplies the calculated life of a ball bearing by eight. That relationship is usually the most useful thing this calculation tells you.
L10 is the basic rating life defined by ISO 281: the number of revolutions that 90% of a group of identical bearings will complete or exceed before the first evidence of material fatigue. It is a statistical figure for a population, not a prediction for your individual bearing — 10% of bearings are expected to fail before it, by definition.
Where do I find the C and P values to enter?
C, the basic dynamic load rating, is published by the manufacturer for every bearing in its catalog or datasheet — it is a property of that specific part, so this tool asks you for it rather than guessing. P is the equivalent dynamic bearing load, which you calculate from the actual radial and axial loads on the bearing using the X and Y factors from the same datasheet. For a purely radial load on a deep-groove ball bearing, P equals the radial load.
Why is the exponent different for ball and roller bearings?
ISO 281 specifies a life exponent p of 3 for ball bearings and 10/3 for roller bearings, reflecting the difference between point contact and line contact in the rolling elements. Using the wrong exponent changes the answer substantially, so the bearing type selector matters.
Why does my bearing not last as long as the calculation says?
Basic rating life assumes good lubrication, clean conditions, correct mounting, no misalignment, and that the load you entered is the real operating load. In practice the great majority of bearing removals are caused by lubrication problems, contamination, misalignment, or mounting damage — not by the fatigue mechanism L10 models. Treat the result as a way to compare candidate bearings under identical assumptions, not as a service-life forecast.
What does the reliability setting change?
It applies the ISO 281 a1 life-adjustment factor, which rescales the answer from the default 90% reliability to a higher one. Requiring that 99% of bearings survive rather than 90% cuts the calculated life to a quarter — which is why the required reliability should be a deliberate decision on critical equipment.
Can KKM Solutions help select or source the bearing?
Yes — send the application details and the part numbers you are comparing to [email protected] and our order desk will work through it with you. We source to exact manufacturer specification per order.
