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Equivalent Dynamic Load Calculator - Combined Radial & Axial Bearing Load

Calculate equivalent dynamic load P from combined radial (Fr) and axial (Fa) forces using X and Y load factors

Free equivalent dynamic bearing load calculator for combined radial and axial loading conditions. When a bearing carries both radial force (Fr) and axial force (Fa), the equivalent dynamic load P determines the effective load for bearing life calculations. The formula is: P = X · Fr + Y · Fa, where X is the radial load factor and Y is the axial load factor. These factors depend on the bearing type, contact angle, and the ratio of Fa to Fr relative to the threshold value e. This calculator handles deep groove ball, angular contact ball (15°, 25°, 40°), cylindrical roller, tapered roller, and spherical roller bearings. Enter your radial and axial loads and the bearing type to get the correct P value for use in the L10 life formula. Getting P wrong directly impacts life predictions: overestimating P gives pessimistic (too short) life predictions and leads to oversized bearings; underestimating P gives optimistic predictions and leads to premature failure.

Pro Tip: For deep groove ball bearings with light axial load (Fa/Fr < e), the axial component has no effect on equivalent load and P simply equals Fr. Many applications fall into this category. Check the Fa/Fr ratio before spending time on X and Y factors.

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Equivalent Dynamic Load Calculator
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How It Works

  1. Enter Radial Load Fr

    Input the radial force acting on the bearing in kN or lbf. Radial load acts perpendicular to the shaft axis. For shaft-mounted bearings, this includes the weight of the shaft assembly, belt tension, gear mesh forces, and any external radial loads.

  2. Enter Axial Load Fa

    Input the axial (thrust) force acting on the bearing. Axial load acts parallel to the shaft axis. Sources include gear mesh thrust components, impeller thrust, thermal growth pushing on fixed bearings, and external axial forces.

  3. Select Bearing Type

    Choose the bearing type. Each type has different X and Y factors. Angular contact bearings have fixed contact angles that determine Y. Tapered roller bearings have Y values specific to the cup angle. Deep groove ball bearings use Y values that depend on the Fa/C0 ratio.

  4. Review Load Factors and P

    The calculator shows the Fa/Fr ratio, the threshold value e, and the resulting X and Y factors. It then calculates P = X·Fr + Y·Fa. Use this P value in the L10 life formula with the bearing dynamic load rating C.

Built For

  • Mechanical engineers calculating bearing loads for fan, pump, and gearbox applications
  • Reliability engineers verifying load assumptions used in bearing life predictions
  • Maintenance teams investigating premature bearing failure by back-calculating actual loads
  • Students working through bearing selection problems in machine design courses
  • Application engineers comparing bearing types for combined-loading conditions

Frequently Asked Questions

X is the radial load factor and Y is the axial load factor. They convert the actual combined load into an equivalent pure radial load that would produce the same bearing life. For deep groove ball bearings under light axial load, X = 1 and Y = 0 (axial load is ignored). As the axial-to-radial ratio increases past the threshold e, X drops to about 0.56 and Y increases to 1.0 to 2.3, meaning the axial load becomes the dominant factor in bearing life.
The threshold value e is listed in bearing manufacturer catalogs alongside the X and Y factors for each bearing series. For deep groove ball bearings, e depends on the Fa/C0 ratio (axial load relative to the static load rating). For angular contact and tapered roller bearings, e is fixed by the contact angle. This calculator includes built-in e values for common bearing configurations.
If the axial load is zero, P equals Fr for all bearing types. You can skip this calculator and enter Fr directly as P in the bearing life formula.
Higher contact angles increase the bearing ability to carry axial loads but decrease radial capacity. A 15-degree angular contact ball bearing has Y around 1.6. A 40-degree bearing has Y around 0.76. The higher contact angle carries more axial load for the same equivalent P, but generates more heat and has a lower radial load rating.
Disclaimer: X and Y factors used in this calculator are representative values for common bearing series. For exact values, consult your bearing manufacturer's catalog for the specific bearing number. Factors vary by internal geometry and can differ between manufacturers.

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