Bearing L10 life
Rating life in hours from the bearing’s dynamic capacity, the actual load, and the speed — the load-cubed relationship that shows why a small overload wrecks bearing life.
Bearing L10 rating life · ball & roller bearings
L10h = (10⁶ / 60N)(C/P)^p · p = 3 ball, 10/3 roller
What this gives you
This is the L10 rating life of a rolling-element bearing — the fatigue life that 90 percent of a batch of identical bearings will reach or exceed before the first spall appears, running at the load and speed you enter. It is the basic-rating-life figure behind every bearing selection. In millions of revolutions it is L10 = (C/P)p, converted to hours by L10h = (106 ÷ 60N) × (C/P)p, where C is the bearing's dynamic load rating, P the actual equivalent load, N the speed in rpm, and p the life exponent — 3 for ball bearings, 10/3 for roller bearings.
Why a small overload wrecks bearing life
The load ratio is raised to the third power for balls (3.33 for rollers), so life is brutally sensitive to load. Double the load on a ball bearing and it keeps only one-eighth of its hours; a 25 percent overload nearly halves them. That is why the C/P ratio outweighs every other input: pick a bigger bearing that doubles C/P and life climbs eightfold, while overloading that shaves C/P collapses it. Speed scales life linearly — run twice as fast and the hours halve — but load is the exponential lever.
Reliability adjustment and load units
Basic L10 life is a 90 percent-reliability figure — one bearing in ten may fail before it. If you need a higher survival rate, multiply L10 by the life-adjustment factor a1: Lna = a1 × L10. This tool carries the classic reliability steps — L10 (90 %, a1 = 1.0), L5 (95 %, a1 = 0.62), L4 (96 %, a1 = 0.53) and L1 (99 %, a1 = 0.21). Demanding 99 percent reliability instead of 90 percent cuts the usable life to about a fifth, which is why critical machines are sized with a lot of headroom. Because life depends only on the ratio C/P, the load units are cosmetic: enter both C and P in lbf or both in newtons and the hours are identical — the selector just relabels the two fields. The years readout divides the chosen life by 8,760 hours to show it as continuous 24/7 running.
Field note — L10 is a statistical floor, not a wear-out date
L10 means one bearing in ten can fail before this time; it is a 90 percent-reliability figure, not a service interval. It also assumes clean lubrication, good alignment, and no contamination or overheating — the things that actually kill most bearings in the field long before fatigue does. Treat the calculated hours as the ceiling set by fatigue alone: if bearings die well short of L10, look at lubrication, mounting, and contamination before you blame the rating.
Worked example
A ball bearing rated C = 5,000 lbf carrying an equivalent load P = 1,000 lbf at 1,750 rpm: the ratio C/P = 5, so basic life is 53 = 125 million revolutions. In hours that is 106 ÷ (60 × 1,750) × 125 = about 1,190 hours. Swap in a roller bearing (exponent 10/3) at the same rating and life climbs to roughly 2,035 hours, because the steeper exponent rewards the C/P = 5 margin more heavily.