Router Speed Calculator
Find the optimal RPM for your router bit based on bit diameter, material type, and cut type. Use it to prevent burning, tearout, and bit damage on wood, plastic, or metal workpieces.
About this calculator
Router bit tip speed — not RPM alone — determines cut quality and tool life. Larger bits travel farther per revolution, so they require lower RPM to maintain a safe tip speed. The recommended RPM is estimated as: RPM = min(maxRpm, round((9000 × materialFactor × cutFactor) / bitDiameter^0.7)), where materialFactor = 1.0 for wood, 0.8 for plastic, and 0.5 for metal, and cutFactor = 1.0 for roughing or 1.5 for finishing passes. The 0.7 exponent models the non-linear relationship between diameter and required speed reduction. The result is capped at the router's maximum rated RPM to prevent exceeding safe operating limits. Always verify your router bit's maximum rated RPM from the manufacturer before use.
How to use
Example: routing a 2-inch diameter panel-raising bit in wood, finishing pass, on a router with a 22,000 RPM maximum. Step 1 — materialFactor = 1.0 (wood), cutFactor = 1.5 (finishing). Step 2 — bitDiameter^0.7 = 2^0.7 ≈ 1.6245. Step 3 — RPM = round((9000 × 1.0 × 1.5) / 1.6245) = round(13500 / 1.6245) ≈ round(8,310) = 8,310 RPM. Step 4 — min(22,000, 8,310) = 8,310 RPM. Set your variable-speed router to approximately 8,300 RPM for a safe, clean finishing cut.
Frequently asked questions
What RPM should I use for a large router bit like a raised panel cutter?
Large-diameter bits (2 inches or more) generate very high tip speeds at standard router RPMs, creating heat, vibration, and safety risks. Most manufacturers recommend no more than 8,000–10,000 RPM for bits over 2 inches in diameter. This calculator's formula automatically reduces the recommended speed as diameter increases using a power-law relationship. Always check the specific bit's maximum rated RPM printed on the shank or packaging, and never exceed it regardless of what the calculator suggests.
Why does router speed need to change for different materials like plastic vs wood?
Different materials respond differently to cutting speed and heat. Plastics like acrylic can melt and re-weld behind the cutter if RPM is too high, leaving a poor surface and dulling the bit. Metals require much slower speeds to manage heat and avoid work-hardening. Wood is the most forgiving but still benefits from speed tuning — harder species generally prefer lower RPM than softwoods. The material factor in this calculator scales the base speed to account for these differences.
How does cut type (roughing vs finishing) affect the recommended router RPM?
Roughing passes remove large amounts of material quickly, generating more heat and cutting force, so a moderate speed is appropriate. Finishing passes take lighter cuts and benefit from higher RPM, which produces more cutter passes per inch of travel and leaves a smoother surface. This calculator applies a 1.5× multiplier for finishing cuts compared to roughing cuts. In practice, the difference may be 1,000–3,000 RPM depending on bit size, and a smoother finish pass at higher speed often means less sanding afterward.