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.