Bearing L10 Life Calculator — Basic & ISO 281 Modified Bearing Life
Calculate basic L10 bearing life, modified rating life or the required dynamic load rating from bearing load, speed, bearing type, reliability and an optional ISO life modification factor.
Enter the known values and review the calculated result
Input parameters
Use consistent values and select the intended engineering units.
Calculation mode
Bearing model
Equivalent dynamic load
Life requirement
Modified rating life
Results
Calculation tools Save, export and manage your results
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Method, application and limitations
Review the calculation method, intended application and engineering assumptions before using the result in a design decision.
Formula and calculation method
This calculator evaluates rolling-bearing rating life from the basic dynamic load rating C, equivalent dynamic bearing load P and rotational speed n, or solves the same relationship inversely for the required dynamic load rating.
Basic bearing rating life L10
The basic rating life in millions of revolutions is:
L10 = (C / P)p
where:
- L10 = basic rating life [106 revolutions], corresponding to 90% reliability,
- C = basic dynamic load rating of the bearing [N],
- P = equivalent dynamic bearing load [N],
- p = life exponent [-].
The calculator uses:
- p = 3 for ball bearings,
- p = 10/3 for roller bearings.
For constant rotational speed, the basic rating life in operating hours is:
L10h = L10 × 106 / (60n)
where n is rotational speed [rpm].
Equivalent dynamic bearing load
The calculator supports four load-definition modes.
Direct equivalent load:
P = entered P
Pure radial load:
P = Fr
Pure axial load:
P = Fa
Combined radial and axial load:
P = X Fr + Y Fa
where:
- Fr = radial bearing load [N],
- Fa = axial bearing load [N],
- X = radial load factor from the catalogue for the exact bearing [-],
- Y = axial load factor from the catalogue for the exact bearing [-].
The calculator does not determine X, Y or the catalogue load-condition branch automatically. These factors must be selected for the actual bearing and operating condition before using the combined-load mode.
Modified rating life Lnm
When the modified-life model is selected, the calculator applies:
Lnm = a1 × aISO × L10
and therefore:
Lnmh = a1 × aISO × L10h
where:
- a1 = life modification factor for the selected reliability [-],
- aISO = externally determined life modification factor entered by the user [-].
| Required reliability | a1 |
|---|---|
| 90% | 1.00 |
| 95% | 0.64 |
| 96% | 0.55 |
| 97% | 0.47 |
| 98% | 0.37 |
| 99% | 0.25 |
Required dynamic load rating
For a target operating life Ltarget, the required life in millions of revolutions is:
Ltarget,rev = Ltarget × 60n / 106
For the basic-life model:
Crequired = P × Ltarget,rev1/p
For the modified-life model, the required basic L10 before application of the life factors is:
L10,required = Ltarget,rev / (a1aISO)
and:
Crequired = P × L10,required1/p
The calculated Crequired is a minimum mathematical dynamic-rating requirement. A real bearing must be selected from current manufacturer data and separately checked for the other applicable operating and design criteria.
When to use this calculator
Use this calculator to estimate rolling-bearing fatigue rating life or to determine the basic dynamic load rating required for a specified operating-life target.
It is intended for preliminary bearing selection and verification when the equivalent dynamic bearing load and rotational speed can be represented by constant values.
Typical uses
- Calculate basic L10 life in millions of revolutions and operating hours.
- Compare bearing fatigue life at different dynamic load ratings, loads or speeds.
- Calculate modified rating life using a selected reliability factor a1 and a supplied aISO factor.
- Determine the minimum basic dynamic load rating C required for a target bearing life.
- Check whether a calculated basic or modified rating life reaches an entered target life.
- Use a known equivalent dynamic load P directly.
- Use pure radial or pure axial load as P when that simplification is valid for the actual bearing arrangement.
- Calculate P from radial and axial loads when the correct catalogue X and Y factors are already known.
When another analysis is required
This calculator is not a complete bearing-selection tool. It does not determine the correct bearing series, bore size, internal clearance, preload, fits, limiting speed, minimum load, lubrication system or static load capacity.
Variable-load or variable-speed duty should not normally be represented by an arbitrary average load. An appropriate equivalent-duty calculation should first be performed before applying the rating-life equation.
The pure radial and pure axial shortcuts should only be used when the selected bearing type and arrangement can actually carry that load in the assumed manner. For combined loading, use X and Y values from the manufacturer data for the exact bearing and applicable load condition.
How to interpret the result
The main result is a statistical rolling-contact fatigue rating, not a guaranteed operating life of an individual bearing.
Basic rating life L10h
L10h is the calculated basic rating life at 90% reliability, expressed in operating hours at the entered constant rotational speed. Increasing C increases calculated life, while increasing P or rotational speed reduces life expressed in hours.
Because life depends on (C/P)p, load changes have a strong nonlinear effect. For example, the exponent is 3 for ball bearings and 10/3 for roller bearings.
Modified rating life Lnmh
When the modified model is selected, Lnmh is obtained by multiplying the basic life by a1aISO. A reliability requirement above 90% reduces a1 below 1.0. The effect of aISO depends entirely on the externally determined value entered by the user.
The calculator does not derive aISO from lubrication, contamination, fatigue load limit or bearing-specific operating data. The entered value therefore has to be appropriate for the exact bearing and application.
Required dynamic load rating Crequired
Crequired is the minimum basic dynamic load rating calculated from the entered equivalent load, speed, target life and selected life model. An available bearing should be selected using its current manufacturer-published dynamic rating and then checked against all other applicable design requirements.
Life target and status
When a target life is entered in life-calculation mode, the calculator compares the applicable calculated life with that target:
- Life / target ≥ 1 means the evaluated rating-life requirement is satisfied.
- Life / target < 1 means the calculated rating life is below the entered target.
- Life margin > 0 means calculated life exceeds the target by that number of hours.
- Life margin < 0 indicates a shortfall relative to the target.
A satisfactory target-life result does not confirm complete bearing suitability. Static safety, peak and shock loads, limiting speed, minimum load, lubrication, contamination, temperature, fits, internal clearance, mounting, alignment and other failure mechanisms may still require verification.
C/P and P/C ratios
The C/P ratio is the principal load-to-capacity ratio in the rating-life equation. A larger C/P ratio produces a longer calculated fatigue life.
P/C expresses the applied equivalent dynamic load relative to the bearing dynamic rating. In the modified-life model, the implemented calculation raises a warning when P/C > 0.5. This warning indicates that the modified-life equation is being used outside the heavy-load applicability condition represented by the calculator and should not be treated as a normal validated modified-life result.
Calculation example
Example: modified rating life of a ball bearing with a target-life check.
A ball bearing operates at 1500 rpm. Its basic dynamic load rating is C = 30 kN and the already-determined equivalent dynamic bearing load is P = 5 kN. A 95% reliability level is required, and an externally determined aISO value of 1.50 is used. The target rating life is 2000 h.
1. Input data
- Bearing type: ball bearing
- p = 3
- C = 30 kN
- P = 5 kN
- n = 1500 rpm
- Reliability = 95%
- a1 = 0.64
- aISO = 1.50
- Ltarget = 2000 h
2. Basic L10 life
C/P = 30 / 5 = 6
L10 = 63 = 216 × 106 revolutions
3. Convert basic life to operating hours
L10h = 216 × 106 / (60 × 1500)
L10h = 2400 h
4. Modified rating life
The combined life factor is:
a1aISO = 0.64 × 1.50 = 0.96
Therefore:
Lnmh = 0.96 × 2400 = 2304 h
5. Compare with the target life
Life / target = 2304 / 2000 = 1.152
Life margin = 2304 − 2000 = 304 h
The evaluated modified rating-life requirement is therefore satisfied because the calculated life exceeds the 2000 h target.
6. Dynamic rating required for the same target
The target operating life corresponds to:
Ltarget,rev = 2000 × 60 × 1500 / 106 = 180 × 106 revolutions
The required basic life before application of the modification factors is:
L10,required = 180 / 0.96 = 187.5 × 106 revolutions
Thus:
Crequired = 5 × 187.51/3 = 28.62 kN
The entered 30 kN dynamic rating is greater than the calculated 28.62 kN minimum for this specific rating-life target.
Engineering limitation: this result evaluates rolling-bearing fatigue rating life only. It does not verify static capacity, lubrication, contamination, mounting, clearance, speed limits, peak loading or other application-specific requirements.
Assumptions and limitations
The calculation is a rolling-bearing rating-life model and should not be interpreted as a complete prediction of real bearing service life.
- The basic life relationship uses L10 = (C/P)p.
- The calculator uses p = 3 for ball bearings and p = 10/3 for roller bearings.
- Basic L10 represents a 90% reliability rating-life quantity.
- Rotational speed is assumed constant when converting life in revolutions to operating hours.
- The equivalent dynamic load P is assumed to represent the governing dynamic duty for the life calculation.
- If P is entered directly, its prior derivation is assumed to be correct.
- For pure radial loading the calculator sets P = Fr; this is only appropriate when the bearing and load case permit that simplification.
- For pure axial loading the calculator sets P = Fa; this is only appropriate when the bearing arrangement is intended to carry the applicable axial load.
- For combined loading the calculator uses P = XFr + YFa. It does not determine X, Y, the limiting ratio e or the applicable catalogue branch.
- C, X and Y should come from current manufacturer data for the exact bearing designation and operating condition.
- The modified-life calculation uses Lnm = a1aISOL10.
- aISO is an input to this calculator. It is not calculated from lubricant viscosity, contamination level, fatigue load limit or other bearing-specific parameters.
- The calculator warns in the modified-life model when P/C exceeds 0.5.
- The model does not calculate equivalent life for variable-load or variable-speed duty cycles.
- The calculated Crequired is a mathematical minimum dynamic rating, not a complete bearing-selection approval.
Checks outside this calculator
Depending on the application, additional verification may be required for basic static load rating C0, equivalent static load P0, static safety factor, minimum load, peak and shock loads, limiting or reference speed, lubrication, contamination, temperature, sealing, fits, internal clearance, preload, mounting accuracy, shaft and housing stiffness, misalignment, wear, corrosion and electrical damage.
Actual bearing life can differ substantially from calculated rating life when operating conditions, lubrication, installation or failure mechanisms differ from the assumptions of the rating-life model.
Frequently asked questions
L10 is the basic rolling-bearing rating life associated with 90% reliability. It is expressed in millions of revolutions, or as L10h in operating hours at a specified rotational speed. It is a statistical fatigue rating and not a guaranteed service life for an individual bearing.
The calculator uses L10 = (C/P)p, where C is the basic dynamic load rating, P is the equivalent dynamic bearing load and p is the life exponent. The exponent is 3 for ball bearings and 10/3 for roller bearings.
For constant rotational speed n, the calculator uses L10h = L10 × 106 / (60n). Therefore, for the same life in revolutions, a higher rotational speed produces fewer operating hours.
C is the basic dynamic load rating used in the bearing fatigue-life equation. C0 is the basic static load rating and is used for a different static-load verification. This calculator uses C and does not perform a C0 static safety check.
P is the constant equivalent dynamic load used in the rating-life equation. The calculator can accept P directly, use P = Fr for an applicable pure radial case, use P = Fa for an applicable pure axial case, or calculate P = XFr + YFa when catalogue X and Y factors are supplied.
X and Y are bearing-specific equivalent-load factors. They should be taken from manufacturer data for the exact bearing and applicable radial-to-axial load condition. This calculator does not determine the factors or select the correct catalogue branch automatically.
L10 is the basic rating life at 90% reliability. The modified result Lnm applies the factors a1 and aISO through Lnm = a1aISOL10. In this calculator, a1 is selected from the required reliability and aISO is entered by the user.
aISO is a life modification factor used in the modified rating-life model. This calculator does not derive it from lubrication, contamination or bearing fatigue-limit data, so the value must be obtained from an appropriate bearing calculation or manufacturer method for the actual application.
Select the required dynamic load rating mode and enter the equivalent dynamic load P, rotational speed, target operating life and bearing type. For the modified model, also select reliability and enter aISO. The result Crequired is the minimum calculated dynamic rating for that life condition.
No. It means only that the evaluated rating-life criterion is satisfied under the entered assumptions. Static load capacity, shock loads, speed, minimum load, lubrication, contamination, temperature, fits, clearance, mounting, alignment and other application requirements may still need separate verification.
Not generally. Bearing fatigue damage is nonlinear with load, so an arithmetic average force may not represent the correct equivalent dynamic duty. For a repeating variable-load or variable-speed cycle, determine an appropriate duty-equivalent bearing load and speed before using this calculator.
The implemented modified-life model treats P/C > 0.5 as a heavy-load condition outside the applicability limit represented by the calculation. The result should therefore be reviewed with the bearing manufacturer's calculation method rather than treated as a normal modified-life prediction.