Bearing Defect Frequency Calculator

Calculate BPFO, BPFI, BSF, and FTF from bearing geometry and shaft speed. Select a common bearing or enter custom dimensions.

Bearing Parameters

0° for deep-groove ball bearings and cylindrical rollers

Results

Enter bearing parameters and click Calculate.

How This Calculator Works

This calculator uses the standard geometric formulas for rolling-element bearing defect frequencies. All four frequencies — BPFO, BPFI, BSF, and FTF — are functions of the bearing's internal geometry and shaft rotational speed.

The preset bearing models use geometry data from published manufacturer specifications. For bearings not listed, select "Custom / Manual Entry" and enter the parameters from the bearing datasheet. The pitch diameter can be approximated as (bore + OD) / 2 if not directly listed.

For a detailed walkthrough of each formula with worked examples, see How to Calculate Bearing Defect Frequencies from a Datasheet.

Formulas Used

BPFO (Outer Race)

BPFO = (N / 2) × fr × (1 - (Bd / Pd) × cos α)

BPFI (Inner Race)

BPFI = (N / 2) × fr × (1 + (Bd / Pd) × cos α)

BSF (Ball Spin)

BSF = (Pd / (2 × Bd)) × fr × (1 - (Bd / Pd)² × cos² α)

FTF (Cage)

FTF = (fr / 2) × (1 - (Bd / Pd) × cos α)

Important Notes

  • Slip: Real bearings experience 1–3% slip under light load, which reduces actual defect frequencies slightly below calculated values. Monitor a ±3% band around each frequency.
  • Variable speed: All defect frequencies scale linearly with shaft RPM. For VFD-driven equipment, recalculate at each operating speed.
  • Harmonics: As defects grow, energy appears at 2×, 3×, and higher multiples of the fundamental defect frequency. Inner race defects produce sidebands at shaft speed around BPFI.
  • Contact angle: Use 0° for deep-groove ball bearings and cylindrical rollers. Angular contact bearings typically use 15°, 25°, or 40°. Tapered roller bearings require the effective contact angle from the manufacturer.