Bearing Capacity Calculator
Estimate dynamic rating margin, adjusted bearing life, required C rating, equivalent load, static C0 safety ratio, and target L10 fit for ball and roller bearings.
Bearing Presets
Calculator Inputs
Bearing life result
Enter bearing ratings, load, speed, and target life.
Formulas Used
P = XFr + YFa, or direct P. Design load = P x application factor.
L10 million rev = (C / Pdesign)^p. Ball p = 3; roller p = 10/3.
Lna hours = a1 x L10 x 1,000,000 / (60 x RPM).
Creq = Pdesign x (target million rev / a1)^(1/p).
P0 = max(Fr, 0.6Fr + Y0Fa) x application factor.
s0 = C0 / P0. Compare it with the chosen target ratio.
Bearing Type Spec Grid
Reference Tables
| Bearing type | Typical use | Exponent p | Default X | Default Y | Static Y0 |
|---|---|---|---|---|---|
| Deep groove ball | Motors, fans, general shafts | 3.00 | 1.00 | 0.00 to 1.60 | 0.50 |
| Angular contact ball | Spindles, pumps, combined load | 3.00 | 0.56 | 1.40 | 0.50 |
| Tapered roller | Wheel hubs, gearboxes | 3.33 | 0.40 | 1.50 | 0.50 |
| Spherical roller | Conveyors, crushers, misalignment | 3.33 | 0.67 | 2.30 | 2.80 |
| Cylindrical roller | Gear shafts, radial load | 3.33 | 1.00 | 0.00 | 0.50 |
| Needle roller | Compact radial packages | 3.33 | 1.00 | 0.00 | 0.50 |
| Thrust bearing | Axial dominant load | 3.00 or 3.33 | 0.00 | 1.00 | 1.00 |
| Reliability | a1 factor | Meaning | Design effect |
|---|---|---|---|
| 90% | 1.00 | Standard L10 rating basis | No life reduction |
| 95% | 0.62 | Higher confidence requirement | Required C rises |
| 96% | 0.53 | Common reliability step | Less adjusted life |
| 97% | 0.44 | Conservative machine design | More C margin needed |
| 98% | 0.33 | Critical duty estimate | Large life reduction |
| 99% | 0.21 | Very high reliability target | Much larger C rating |
| Application | Factor | Example | How it changes result |
|---|---|---|---|
| Smooth | 1.00 | Balanced electric motor | Catalog load unchanged |
| Light shock | 1.10 | Fan, light pump | Slightly higher P |
| Moderate shock | 1.25 | Conveyor, light gearbox | Shorter predicted life |
| Heavy shock | 1.50 | Ag drive, intermittent load | Requires higher C |
| Severe shock | 1.75 | Crusher, uneven load | Large dynamic penalty |
| Impact | 2.00 | Unknown or impact duty | Use with caution |
| Static safety s0 | Typical interpretation | Risk if low | Practical response |
|---|---|---|---|
| Below 1.0 | Static capacity is likely undersized | Permanent raceway denting | Increase C0 or reduce load |
| 1.0 to 1.5 | Light or smooth duty only | Low shock reserve | Check peak loads carefully |
| 1.5 to 2.0 | Common general-purpose target | Moderate reserve | Often acceptable for steady duty |
| 2.0 to 3.0 | Better shock and start-stop margin | Lower brinelling risk | Good for harsher duty |
| Above 3.0 | Strong static reserve | Oversize may affect package | Check speed, fit, and cost separately |
Tips and Safety
This calculator estimates bearing rating capacity from simplified ISO-style life relationships. It does not replace manufacturer catalog selection, lubrication analysis, mounting fit checks, thermal limits, or speed-limit review.
Selecting a bearing is a necessary part of the design of any machines that incorporates a rotating element. A bearing is the component of the machine that help to allow the rotating portion of the machine to rotate smooth and efficiently. If the bearing is sized correctly for the machine, the bearing will be able to operate for a long period of time.
However, if the bearing is sized incorrectly, the bearing will experience additional heat production, create noise for the machine, or the machine may even shut down due to the bearing issue. To select a bearing, there are two values that is required from a bearing catalog. These two values are the dynamic capacity of the bearing, which is represented by the value C, and the static capacity of the bearing, which is represented by the value C0. The dynamic capacity is the load that the bearing can handle for a specific number of revolutions before the metal of the bearing begin to develop fatigue.
How to Choose the Right Bearing
The static capacity is the load that the bearing can handle when the bearing is not rotating, and which will not create dent in the raceways of the bearing. These two values are entered into a calculator along with the forces and the speeds at which the machine will operate to determine whether or not the bearing will be appropriate for that design. There are two different types of loads that can act upon a rotating bearing: radial load and axial load.
Radial loads are force that act directly through the shaft of the rotating component of the machine. Axial loads are those forces that act along the axis of the shaft. Most rotating machine component experience both radial and axial loads simultaneously.
Therefore, the radial and axial loads are combined into a single value: the equivalent dynamic load. This value is calculated with the use of two different factor: X and Y. These factors are not the same for all types of bearings; for instance, deep-groove bearings have different X and Y factors than angular-contact bearings due to the difference in contact angles between the two types of bearings. Following the calculation of the equivalent dynamic load for the bearing, an application factor multiplies that value.
This factor accounts for any unexpected event that may occur that are outside of those described in a standard load diagram for the machine. For instance, a bearing that is used in a smooth electric motor may have an application factor of 1.0, but a bearing that is used in a conveyor belt may have an application factor of 1.25 or 1.5 due to the expected shocks that may occur in the conveyor belt. This adjusted load can then be used to calculate the life of the bearing.
Bearing life is often expressed as the L10 life of the bearing, which is the number of revolutions that 90 percent of a group of identical bearings will last. To account for higher reliability than the L10 life, a reliability factor, which is represented as a1, can be used. If higher reliability is desired for the bearing, the predicted life of the bearing will decrease because more capacity must be provided to meet the higher reliability target.
Another factor to consider in the calculation of bearing life is the speed at which the bearing will operate. Because the number of revolutions is often expressed as the life of the bearing, such as 20 million revolutions, the speed of the bearing will impact the number of hour that the bearing will last. For instance, a bearing that has a life of 20 million revolutions may last for hundreds of hour at a low speed, but will last for only hundreds of hour at a high speed.
Thus, high speeds will reduce the life of the bearing in comparison to lower speeds, requiring larger bearings for those high-speed machine. Another factor to consider is the static safety ratio. This ratio is created by dividing the static capacity of the bearing by the peak equivalent static load.
This factor is considered in situations in which the machine may sit idle or turn on and off many time during its operation. In these situations, the elements of the bearing may create plastic deformation in the bearing raceways. Plastic deformation is the action of the rolling elements of the bearing creating dent in the raceways.
A static safety ratio of 1.0 or below will result in potential dent being created in the bearing raceways. A static safety ratio between 1.5 and 2.0 is generally considered to provide enough of a safety margin to prevent plastic deformation in most machine design and manufacturing scenario. Different types of bearings have different mathematical exponent in their calculations of life.
For instance, ball bearings have an exponent of three in their calculation of life, but roller bearings have an exponent of 10/3. This relationship between the two types of bearings is due to the fact that a roller bearing is a line contact while a ball bearing is a point contact. Additionally, a tapered roller bearing can handle both radial and axial loads, which is why it is different than calculations for bearings like deep-groove ball bearings.
While the calculator allows for the selection of bearings based off a number of different factors, the calculator does not account for factors like temperature, lubrication and cleanliness, or the mounting fits of the bearing. The factors of temperature, lubrication and cleanliness can be accounted for in the engineer’s own judgment. For instance, many engineer will make the mistake of using only the C and C0 values without considering that those loads are established with the assumption of standard lubrication for the bearing.
In addition, many engineers will also forget to apply the application factor when performing a static safety calculation. Finally, many engineers will set a reliability target without understanding that using a high reliability target will impact the size of the bearing that is selected. Overall, the calculator is a helpful tool that allows engineers to test the impact of various factors upon the selection of bearings for a machine.
For instance, each engineer can adjust the reliability target that is entered into the calculator to see how that alters the C value for the bearing. Additionally, the application factor could be adjusted to evaluate the impact upon the static safety margin. A large margin for both dynamic life and static safety indicates that the bearing is unlikely to fail quick.
A narrow margin for either dynamic life or static safety indicates that a careful examination of the lubrication and the loads that are to be experienced by the bearing will be necessary to ensure that the bearing is sufficient for the machine that is to be constructed.
