Milling · Drilling · Turning
Speeds and Feeds Calculator
The core machining math in one place: spindle speed from cutting speed and diameter, cutting speed from RPM, and table feed from chip load per tooth. Works in metric (m/min, mm) and imperial (SFM, inch) with instant unit conversion.
Cutting speed → RPM
n = Vc·1000 / (π·D)RPM → cutting speed
Vc = π·D·n / 1000Chip load → table feed
vf = fz · z · nTable feed → chip load
fz = vf / (z · n)Formulas used
Spindle speed: n (RPM) = Vc × 1000 / (π × D) · n = SFM × 12 / (π × D in inches)
Cutting speed: Vc (m/min) = π × D × n / 1000 · SFM = π × D(in) × n / 12
Table feed: vf = fz × z × n Feed per rev: fn = fz × z
Frequently asked questions
What is the formula for RPM from SFM?
RPM = (SFM × 12) / (π × diameter in inches). In metric, RPM = (cutting speed in m/min × 1000) / (π × diameter in mm).
How do I calculate feed rate for milling?
Table feed vf = feed per tooth (fz) × number of teeth (z) × spindle speed (n). For drilling and turning use feed per revolution: vf = fn × n.
What cutting speed should I use?
It depends on tool material, workpiece and operation. Carbide on mild steel typically runs 120–250 m/min (400–800 SFM); HSS about a quarter of that. Always start from your tool supplier's recommendation.
Why is my calculated RPM different from the machine setting?
Machines offer discrete speeds — pick the nearest available RPM and recompute the actual cutting speed with the RPM → cutting speed calculator to confirm you are within range.