CNC Feeds & Speeds Calculator
Use this tool to estimate spindle RPM, feed rate, and optional material removal rate (MRR). Start with a material preset, then fine-tune based on your machine, tool, and setup rigidity.
Recommended Spindle Speed: - RPM
Recommended Feed Rate: - IPM
Why feeds and speeds matter
If you run too slow, the cutter rubs and overheats. If you run too fast, you can chip the edge, lose accuracy, and break tools. A good feeds-and-speeds starting point helps you cut cleaner, hold tolerance, and extend tool life.
This calculator gives practical baseline values for CNC milling and router work. It is intentionally simple: you enter tool diameter, flute count, cutting speed, and chip load. Then it returns spindle RPM and feed rate.
Core formulas used by this calculator
RPM = (SFM × 3.82) ÷ Tool Diameter (in)
Feed (IPM) = RPM × Flutes × Chip Load (in/tooth)
RPM = (1000 × Cutting Speed m/min) ÷ (π × Tool Diameter mm)
Feed (mm/min) = RPM × Flutes × Chip Load (mm/tooth)
If you provide axial depth and radial width of cut, the tool also estimates material removal rate (MRR):
- Imperial: MRR = Feed (IPM) × Axial DOC (in) × Radial WOC (in), in³/min
- Metric: MRR = Feed (mm/min) × Axial DOC (mm) × Radial WOC (mm), mm³/min (plus cm³/min)
How to use this CNC calculator correctly
1) Choose units and a material preset
Pick Imperial or Metric first. Then choose a material preset to auto-fill reasonable starting values for cutting speed and chip load.
2) Enter your real cutter and setup values
Tool diameter and flute count must match the actual tool in the spindle. If the tool is long-stickout, in a holder extension, or your machine is light-duty, reduce starting chip load 10–30%.
3) Calculate, then tune during a test cut
Use the result as a first pass. During the test cut, watch spindle load, listen for chatter, and inspect chips/surface finish.
- Chatter or squeal: reduce RPM slightly and/or reduce radial engagement.
- Blue chips or edge wear: reduce cutting speed, improve coolant/air blast.
- Powdery chips (rubbing): increase feed per tooth slightly.
Quick starting guidance by material
Aluminum
Usually supports higher surface speed. Keep chips clearing with air blast or coolant to avoid recutting and built-up edge.
Steel
Lower surface speed than aluminum, generally steadier chip load. Rigid setup and proper coolant strategy are key.
Stainless steel
Work-hardens easily. Avoid rubbing by maintaining chip load. Use sharp tools and consistent engagement.
Titanium
Runs hot at the cutting edge. Use conservative speed, stable toolpath, and good heat management.
Common mistakes when setting feeds and speeds
- Using manufacturer values without adjusting for machine rigidity.
- Ignoring flute count changes when calculating feed rate.
- Using very high RPM with too low feed (rubbing instead of cutting).
- Not reducing values for deep stickout or weak workholding.
- Failing to validate with a short test pass before full production.
Final note
This calculator is a practical baseline tool, not a substitute for toolmaker data or shop testing. Always prioritize safe workholding, correct tool clamping, and machine limits. Start conservative, then optimize with measured adjustments.