Mechanical · Rotating equipment
Bearing Life Calculator
ISO 281 L₁₀ rating life — pick a standard bearing or enter dimensions and loads manually. Derive P from radial + axial forces, estimate C from geometry, or switch to plain bearings for PV duty.
Bearing selection
Bearing dimensions
manual entryEnvelope size (d, D, B). Pitch diameter Dpw is auto-filled as (d + D) / 2 — enter ball count Z and ball diameter Dw in the ratings section to derive C.
Rolling elements & ratings C, C₀
Rolling elements — custom C & C₀
Z and Dw set ISO 281 dynamic C and ISO 76 static C₀. C₀ is required for deep-groove equivalent load P when you enter Fr and Fa (Fa/C₀ factors). Envelope d, D, B alone cannot derive ratings.
C ≈ —·C₀ ≈ —
ISO 281 / ISO 76 estimates (±10–20% vs catalogue). Updates as you change Z or Dw.
Operating load & speed
Life adjustment (optional)
Results
Basic rating life
L₁₀ = (C / P)³
Enter the dynamic rating C, equivalent load P, and speed — the bearing diagram tracks your inputs.
Bearing schematic
ISO 281 basic rating life from the dynamic load rating, equivalent load, and speed.
The basic rating life L10 is the number of revolutions (or operating hours) that 90% of a group of identical bearings will reach or exceed before the first signs of rolling-contact fatigue. In other words, 10% are expected to have failed by L10, which is why it is also called the “B10” life. It is the standard way to compare and size rolling bearings under a steady load and speed.
Life is driven by the ratio of the basic dynamic load rating C (a catalog value for each bearing) to the equivalent dynamic load P actually carried, raised to the load–life exponent p:
- p = 3 for ball bearings (point contact)
- p = 10/3 for roller bearings (line contact)
Convert to hours at constant speed n (rpm):
The modified rating life adds reliability and ISO factors:
C and P are the basic dynamic load rating and equivalent dynamic load (kN); n is speed (rpm); a₁ is the reliability factor (1.0 for 90% / L10); aISO is the life modification factor for lubrication and contamination (use 1.0 unless you have a full ISO 281 analysis).
When a bearing carries both radial (Fr) and axial/thrust (Fa) load, the equivalent dynamic load combines them with the radial/axial factors X and Y:
X and Y switch at the limit ratio e = Fa/Fr. For deep-groove ball bearings e and Y depend on Fa/C0 (so the static rating C0 is needed). Angular-contact ball bearings use fixed factors (e ≈ 1.14, X = 0.35, Y = 0.57). Tapered rollers derive e and Y from the contact angle. Standard cylindrical rollers carry radial load only, so P = Fr.
ISO 281 derives dynamic C and ISO 76 derives static C₀ from the same internal geometry:
Z is the number of balls, Dw the ball diameter, α the contact angle and i the number of rows. Life uses C only in L₁₀ = (C/P)^p, but deep-groove equivalent load P needs C₀ for Fa/C₀ factors when you enter Fr and Fa. For a custom design, use the “Rolling elements” section: enter number of balls Z and ball diameter Dw, keep “Use this C for life” checked, and the calculator updates C live (typically within ±10–15% of a catalogue value).
Plain (sleeve / journal) bearings do not fail by rolling-contact fatigue, so ISO 281 does not apply. Instead they are limited by the PV factor — bearing pressure times sliding velocity:
- Pressure P = W / (d · L) on the projected area
- Velocity V = π · d · n / 60000 (m/s, with d in mm and n in rpm)
- PV = P · V, compared against the material’s PV limit
With a specific wear rate K and an allowable wear depth, the plain-bearing mode also estimates a wear life from the Archard wear model. Use the “Plain bearing” method at the top of the calculator.
A deep-groove ball bearing has a dynamic rating C = 30 kN and carries an equivalent load P = 5 kN at n = 3000 rpm.
- Load ratio C/P = 30 / 5 = 6
- L₁₀ = 6³ = 216 million revolutions
- L₁₀h = 216 × 10⁶ / (60 × 3000) = 1200 hours
With a₁ = aISO = 1.0 the adjusted life equals the basic life. The 1200 h result sits just above the 1000 h rule of thumb, so for continuous duty you would likely choose a larger bearing.
- What is the difference between C and P?
- C is the basic dynamic load rating from the bearing catalog — the load giving one million revolutions of L10 life. P is the equivalent dynamic load your application actually applies, combining radial and axial components.
- Why is the exponent different for ball and roller bearings?
- Roller bearings make line contact rather than point contact, spreading load over a larger area. ISO 281 captures this with p = 10/3 for rollers versus p = 3 for balls.
- What does the a1 reliability factor do?
- a₁ scales life for reliabilities other than 90%. a₁ = 1.0 gives L10 (90%); lower values such as 0.62, 0.53, 0.44 and 0.33 correspond to 95%, 96%, 97% and 99% reliability.
- Is this the same as the SKF bearing life calculation?
- The basic L10 formula is identical across manufacturers (it is ISO 281). SKF’s SKF Rating Life adds a detailed aISO factor from lubrication, contamination and fatigue load limit; here aISO is a single input you can set manually.
- Assumes constant load and constant speed; use equivalent values for varying duty.
- Does not size the equivalent load P from radial/axial components — compute P separately.
- aISO is treated as a single user input, not derived from lubrication and contamination.
- Ignores temperature, misalignment, and static load (C₀) limits.
- Fatigue life is statistical; individual bearings may fail earlier or later than L₁₀.