KEVOS® MAKEOS · Power Transmission
Rolling Bearing Static Equivalent Load and Static Safety Factor
What static equivalent load does my ball or roller bearing carry under combined radial and axial loads, and is its static load rating enough for the static safety factor I need?
Static equivalent loads of ball and roller bearings by the AFBMA formulas the handbook gives: radial bearings Po = Xo Fr + Yo Fa but not less than Fr, with Xo and Yo for radial contact, angular contact (15° to 40°, interpolated), self-aligning ball and self-aligning or tapered roller bearings in single or double row (and duplex pairs); thrust bearings Poa = Fa + 2.3 Fr tan α, with the range of Fr ÷ Fa for which it holds; and the static safety factor Co ÷ Po against the value you require.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Bearing type | choice | Kind of bearing, which sets the static load factors. |
| Rows or mounting | choice | Single row or a tandem pair (single row factors), or double row or a back-to-back or face-to-face pair (double row factors); give the total loads on a pair. |
| Thrust bearing direction | choice | Single or double direction thrust bearing; used for thrust bearings only. |
| Nominal contact angle α | ° | Nominal contact angle of the bearing. |
| Radial load Fr | N | Radial load on the bearing (total for a pair). |
| Axial load Fa | N | Axial load on the bearing (total for a pair). |
| Rating check | ||
| Basic static load rating Co (or Coa) | kN | Basic static load rating of the bearing, from the maker’s catalogue or the static rating formulas. |
| Static safety factor you require | Smallest static safety factor Co ÷ Po you accept for the duty. | |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Bearing type
- What it is
- Kind of rolling bearing, which sets the static load factors used.
- Units and format
- Choose one of 7 options from the list: Radial contact groove ball (α = 0°); Angular contact groove ball; Self-aligning ball; Self-aligning or tapered roller; Radial roller with α = 0° (radial load only); Thrust ball; Thrust roller.
- Example
- The form opens with “Angular contact groove ball” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- Changes Xo and Yo or the thrust formula.
- Get it right
- Use the maker’s description; tapered roller bearings use the roller factors.
What this means: Rows or mounting
- What it is
- Whether one row of rolling elements carries the load, or two rows or a matched pair.
- Units and format
- Choose one of 2 options from the list: Single row, or tandem pair; Double row, or back-to-back / face-to-face pair.
- Example
- The form opens with “Single row, or tandem pair” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- Double row factors raise Xo and Yo.
- Get it right
- A tandem pair counts as single row; back-to-back and face-to-face pairs as double row.
What this means: Thrust bearing direction
- What it is
- Whether a thrust bearing takes axial load in one direction or both.
- Units and format
- Choose one of 2 options from the list: Single direction; Double direction.
- Example
- The form opens with “Single direction” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- Sets the range of Fr ÷ Fa for which the thrust formula holds.
- Get it right
- Only used for thrust ball and thrust roller bearings.
What this means: Nominal contact angle α
- What it is
- Nominal angle between the line of contact and a radial plane of the bearing.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 0° to 90°. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 25° as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sets Yo for angular and roller bearings and the 2.3 Fr tan α term.
- Get it right
- Take it from the bearing catalogue; deep groove ball bearings are 0°.
What this means: Radial load Fr
- What it is
- Force on the bearing at right angles to the shaft axis.
- Units and format
- Enter a number in N: newtons. The form accepts 0 N to 100000000 N. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2000 N as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Raises the static equivalent load; Po is never less than Fr.
- Get it right
- For a matched pair, enter the total radial load on the pair.
What this means: Axial load Fa
- What it is
- Force on the bearing along the shaft axis.
- Units and format
- Enter a number in N: newtons. The form accepts 0 N to 100000000 N. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4000 N as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Raises the static equivalent load through Yo.
- Get it right
- For a matched pair, enter the total axial load on the pair.
Rating check
What this means: Basic static load rating Co (or Coa)
- What it is
- Static load rating of the bearing from the maker or the rating formulas.
- Units and format
- Enter a number in kN: kilonewtons (1 kN = 1000 N). The form accepts 0.000001 kN to 100000 kN. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 30 kN as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Divided by Po to give the static safety factor.
- Get it right
- Use Co for radial bearings and Coa for thrust bearings, in kilonewtons.
What this means: Static safety factor you require
- What it is
- Smallest ratio of static rating to static load that the duty allows.
- Units and format
- Enter a plain number with no unit. The form accepts 0.1 to 20. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Fails the bearing when Co ÷ Po is below it.
- Get it right
- Take it from the bearing maker for the smoothness and shock of the duty.
Method and formulas
- Radial bearings: Po = Xo Fr + Yo Fa, but not less than Fr.
- Radial contact ball: Xo 0.6, Yo 0.5. Angular contact ball, single row: Xo 0.5, Yo 0.47, 0.42, 0.38, 0.33, 0.29, 0.26 at 15°, 20°, 25°, 30°, 35°, 40° (linear between); double row Xo 1 and twice these Yo.
- Self-aligning ball and self-aligning or tapered roller: single row Xo 0.5, Yo 0.22 cot α; double row Xo 1, Yo 0.44 cot α. Radial roller with α = 0° under radial load: Po = Fr.
- Thrust bearings (α < 90°): Poa = Fa + 2.3 Fr tan α; α = 90°: Poa = Fa. Single direction thrust ball valid for Fr ÷ Fa ≤ 0.44 cot α (satisfactory up to 0.67 cot α); thrust roller less accurate when Fr > 0.44 Fa cot α.
- Static safety factor = Co ÷ Po.
- Example: the static equivalent load is 2,520 N, giving a static safety factor of 11.905.
Limitations
- The permissible Fa ÷ Co of radial ball bearings depends on the groove depth and internal clearance; consult the maker.
- Radial roller bearings with α = 0° vary widely in axial capacity; the maker must advise on equivalent load when they carry axial load.
- The static load rating is entered by you; the safety factor you need depends on the duty, quietness and shock.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a bearing under a heavy load while stationary or turning slowly
- Compare single and paired angular contact bearings
- Find the static load on a thrust bearing with some radial load
Who it is for
- Machine designers
- Maintenance engineers
- Reliability engineers
What you get
- Static load factors Xo and Yo
- Static equivalent radial or axial load
- Static safety factor Co ÷ Po
- Validity of the thrust bearing formula
Interpreting the result
- A tandem pair uses single row factors with the total loads; back-to-back and face-to-face pairs use double row factors.
- A static safety factor below the required value means permanent deformation of the raceways is likely.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2417–2419. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These KEVOS® Library readings explain the method this tool uses, with worked examples.
Useful alongside · Library collection
Selecting bearings and lubrication for reliable machines: types, life, fits, sealing and failure causes
In Machine Elements and Mechanical Design
What it covers: Most bearings fail from contamination, poor lubrication or bad fitting, not fatigue. How to choose bearing types, size them for life, fit, seal and lubricate them, and diagnose failures.
KEVOS® tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Rolling Bearing Static Equivalent Load and Static Safety Factor calculator