Router Bit Speed Calculator
Calculate the correct RPM for your router bit diameter.
Running router bits too fast is dangerous — find the safe speed for every bit size.
Router bits have maximum safe RPM ratings based on their diameter. At high RPM, the rim of a large bit can reach dangerous speeds — the centrifugal force can cause the bit to shatter. This is known as the “rim speed” limit.
Maximum rim speed for carbide router bits: approximately 14,000–18,000 metres per minute (230–300 m/s)
Maximum RPM formula: Max RPM = (rim speed × 1000) / (pi × diameter)
Using 14,000 m/min as the conservative safe limit: Max RPM ≈ 4,460,000 / diameter (mm)
Manufacturer recommended maximums:
| Bit Diameter | Max RPM |
|---|---|
| 6 mm (1/4 in) | 30,000+ RPM |
| 12 mm (1/2 in) | 24,000 RPM |
| 20 mm (3/4 in) | 18,000 RPM |
| 32 mm (1-1/4 in) | 16,000 RPM |
| 50 mm (2 in) | 12,000 RPM |
| 75 mm (3 in) panel raising | 10,000 RPM |
| 100 mm (4 in) | 8,000 RPM |
Practical tip: Most fixed-base routers run 22,000–27,000 RPM — fine for small bits but too fast for large panel-raising bits. Variable-speed routers are essential for bits over 32 mm.
Feed rate also matters: Running too slowly causes burning. Moving the router too quickly causes tear-out. The correct feed rate is when the chips are small and even, and the cut surface is clean.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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