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.
Calculate bearing life from C and P values to verify your selection meets the duty cycle
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Pump Affinity Laws Calculator →How It Works
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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.
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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.
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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.
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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
Assumptions
- Equivalent load P = X x Fr + Y x Fa, where X and Y factors are selected based on Fa/Fr ratio and bearing type.
- X and Y factors are representative values for common bearing series; actual values depend on specific bearing geometry.
- For Fa/Fr below the threshold ratio (e), X=1 and Y=0 (radial load dominates).
- Applied loads are steady-state; dynamic or impact loads require application factors before entering this calculation.
Limitations
- Does not determine the axial load induced by radial loads in angular contact or tapered roller bearings.
- Back-to-back and face-to-face duplex arrangements have different X/Y factors not covered in the generic table.
- Four-row tapered roller bearings and multi-row cylindrical roller bearings require manufacturer-specific factors.
- Moment loads and combined loading from shaft bending are not decomposed into radial and axial components.
References
- ISO 281 - Rolling Bearings: Dynamic Load Ratings and Rating Life (X and Y factor methodology)
- SKF Rolling Bearings Catalog - Equivalent Dynamic Bearing Load Calculation
- Timken Engineering Manual - Load Calculation for Tapered Roller Bearings
- NSK Technical Report - Equivalent Load Calculation and Application Factors