Bearing Defect Frequency Calculator
BPFO, BPFI, BSF and FTF fault frequencies from bearing geometry — the fingerprints in a vibration spectrum.
A peak at BPFO with harmonics is the classic early spall signature — and it appears weeks before audible noise. Cage frequency (FTF) sidebands around BPFI usually mean the defect is on the inner race passing in and out of the load zone.
Formula
Note: Condition-monitoring guidance, not a substitute for the machine maker's limits or a qualified vibration analyst on safety-critical equipment.
BPFO, BPFI, BSF and FTF fault frequencies from bearing geometry — the fingerprints in a vibration spectrum. A free cnc machining: speeds, feeds & tool wear tool — no sign-up, no upload, instant results in your browser.
About Bearing Defect Frequency Calculator
Bearing Defect Frequency Calculator computes the governing relationship BPFO = (N/2)·fr·(1−(d/D)cosθ) … standard rolling-bearing kinematics live as you type. A peak at BPFO with harmonics is the classic early spall signature — and it appears weeks before audible noise. Cage frequency (FTF) sidebands around BPFI usually mean the defect is on the inner race passing in and out of the load zone. Defaults are pre-filled with realistic values for this exact scenario, and the worked example substitutes your numbers step by step so the math is never a black box.
How to use Bearing Defect Frequency Calculator
- 1Enter your values — Shaft speed, Number of rolling elements, Ball diameter, Pitch diameter and more (sensible defaults are pre-filled).
- 2Read the live results: BPFO (outer race), BPFI (inner race), BSF (ball spin), FTF (cage).
- 3Check the "with your numbers" line to see BPFO = (N/2)·fr·(1−(d/D)cosθ) … standard rolling-bearing kinematics substituted step by step.
- 4Adjust inputs until the scenario matches yours, then copy or share the result.
Why use Bearing Defect Frequency Calculator?
- ✓Instant, free and private — every calculation runs client-side in your browser; nothing is uploaded
- ✓Built on the stated formula BPFO = (N/2)·fr·(1−(d/D)cosθ) … standard rolling-bearing kinematics with authoritative sources cited on the page (ISO 20816-1 (ex 10816) — Mechanical vibration evaluation; ISO 21940-11 — Rotor balancing; ISO 3685 — Tool-life testing with single-point turning tools)
- ✓A peak at BPFO with harmonics is the classic early spall signature — and it appears weeks before audible noise.
- ✓SI ⇄ Imperial toggle converts your inputs in place, so you can work in the units your drawings use
Frequently asked questions
What formula does the bearing defect frequency calculator use?+
It evaluates BPFO = (N/2)·fr·(1−(d/D)cosθ) … standard rolling-bearing kinematics, exactly as published. Sources: ISO 20816-1 (ex 10816) — Mechanical vibration evaluation; ISO 21940-11 — Rotor balancing; ISO 3685 — Tool-life testing with single-point turning tools. The substituted worked example on the page lets you verify every step against the textbook.
How should I read the result — and how far can I trust it?+
A peak at BPFO with harmonics is the classic early spall signature — and it appears weeks before audible noise. Condition-monitoring guidance, not a substitute for the machine maker's limits or a qualified vibration analyst on safety-critical equipment.
When is this calculator the right tool for the job?+
BPFO, BPFI, BSF and FTF fault frequencies from bearing geometry. Cage frequency (FTF) sidebands around BPFI usually mean the defect is on the inner race passing in and out of the load zone. For neighbouring scenarios, the related tools below cover the same engine with different presets.
Does it support both metric and imperial units?+
Yes — the SI ⇄ Imperial toggle converts the values already in the fields, preserving the physical quantity, so you can flip mid-calculation without re-entering anything.
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