What is bearing L10 life?

L10 life (also called basic rating life) is the number of revolutions that 90% of a sufficiently large group of identical bearings can complete under a given load and speed before the first signs of fatigue appear. It is the standard way manufacturers rate bearing life.

How do you calculate ball bearing life?

For ball bearings, the basic rating life in millions of revolutions is L10 = (C / P)^3, where C is the dynamic load rating and P is the equivalent dynamic bearing load. Life in hours is then L10h = (L10 × 10^6) / (60 × n), where n is speed in rpm.

What is the difference between basic and modified bearing life?

Basic rating life L10 considers only load and speed at 90% reliability. Modified life Lna includes additional factors such as reliability other than 90%, lubrication quality, contamination, and material improvements. It is often expressed as Lna = a1 × aISO × L10, where a1 is a reliability factor and aISO is an application factor.

Does higher speed increase or decrease bearing life?

Higher speed reduces bearing life in hours because the bearing completes more revolutions per hour. For a given L10 in revolutions, life in hours is inversely proportional to speed: doubling the speed halves the life in hours.

Bearing Life Calculator – L10, Modified Life & Reliability

How this bearing life calculator works

This tool implements the standard ISO/ABMA rating life equations used by major manufacturers (SKF, NSK, Timken, etc.) for ball and roller bearings. It focuses on fatigue life under constant load and speed.

1. Basic rating life L10 (90% reliability)

For a constant equivalent dynamic load \(P\) and dynamic load rating \(C\), the basic rating life in millions of revolutions is:

Ball bearings:

\[ L_{10} = \left(\frac{C}{P}\right)^3 \]

Roller bearings:

\[ L_{10} = \left(\frac{C}{P}\right)^{10/3} \]

where:
• \(L_{10}\) = basic rating life [million revolutions]
• \(C\) = dynamic load rating [kN]
• \(P\) = equivalent dynamic bearing load [kN]

2. Life in hours

To convert life from revolutions to hours at speed \(n\) in rpm:

\[ L_{10h} = \frac{L_{10} \times 10^6}{60 \, n} \]

where \(L_{10h}\) is the basic rating life in hours.

3. Reliability factor \(a_1\)

The basic rating life \(L_{10}\) corresponds to 90% reliability. For other reliabilities, ISO/ABMA define a reliability factor \(a_1\). Typical values for ball bearings are:

90% reliability → \(a_1 = 1.00\)
95% reliability → \(a_1 \approx 0.62\)
96% reliability → \(a_1 \approx 0.53\)
97% reliability → \(a_1 \approx 0.44\)
98% reliability → \(a_1 \approx 0.33\)
99% reliability → \(a_1 \approx 0.21\)

The calculator interpolates between these values for any reliability between 90% and 99%.

4. Modified life \(L_{na}\)

A more realistic life estimate includes both reliability and application conditions (lubrication, contamination, material improvements). A common form is:

\[ L_{na} = a_1 \, a_{\mathrm{ISO}} \, L_{10} \]

where:
• \(a_1\) = reliability factor
• \(a_{\mathrm{ISO}}\) = application factor (user input, default 1.0)
• \(L_{na}\) = modified life in million revolutions

Worked example

Assume a deep-groove ball bearing with:

Dynamic load rating \(C = 25\ \text{kN}\)
Equivalent dynamic load \(P = 10\ \text{kN}\)
Speed \(n = 1500\ \text{rpm}\)
Reliability \(R = 95\%\)
Application factor \(a_{\mathrm{ISO}} = 1.0\)

Basic rating life: \[ L_{10} = \left(\frac{25}{10}\right)^3 = 15.625\ \text{million rev} \]
Life in hours: \[ L_{10h} = \frac{15.625 \times 10^6}{60 \times 1500} \approx 173\ \text{h} \]
Reliability factor: for 95% reliability, \(a_1 \approx 0.62\).
Modified life: \[ L_{na} = 0.62 \times 1.0 \times 15.625 \approx 9.69\ \text{million rev} \] \[ L_{nah} = \frac{9.69 \times 10^6}{60 \times 1500} \approx 108\ \text{h} \]

Engineering tips for using bearing life calculations

Use catalogue C and P: Always take \(C\) from the manufacturer’s data and compute \(P\) using their recommended load factors for radial/axial loads.
Check operating conditions: Poor lubrication, contamination, misalignment, and vibration can reduce real life far below calculated L10.
Consider duty cycles: If load or speed varies, compute an equivalent load or use a weighted life calculation rather than a single constant value.
Don’t ignore mounting and preload: Excessive preload or incorrect fits can significantly increase P and reduce life.

FAQ

Is L10 life the same as average bearing life?

No. L10 is a statistical life at 90% reliability. The average life of a bearing population is typically higher (often around 4–5 times L10), but it is not used for design because it is less conservative.

Can I use this calculator for roller bearings?

Yes. Select “Roller bearing (p = 10/3)” at the top. The calculator will use the correct exponent for cylindrical, tapered, or spherical roller bearings, assuming you provide the appropriate dynamic load rating \(C\) and equivalent load \(P\).

What units should I use for C and P?

Enter both \(C\) and \(P\) in kN. If your catalogue values are in N or lbf, convert them to kN before entering. The ratio \(C/P\) is dimensionless, so as long as both are in the same force unit, the life result is valid.

Bearing Life Calculator (Ball Bearings)