CNC Milling Speeds & Feeds Calculator
Enter your cutter diameter, flute count, and either cutting speed and chip load, or spindle speed and feed rate. The calculator converts these into the rest, in the units you choose.
Your milling speeds and feeds
Based on the cutter, cutting data and units entered. These are calculated values, not recommended cutting data or a safety approval.
Calculation summary
| Quantity | Value | Status |
|---|---|---|
| Cutter diameter | 10.00 mm | Entered |
| Flutes / effective teeth | 4 | Entered |
| Cutting speed | 150.0 m/min | Entered |
| Spindle speed | 4,775 RPM | Calculated |
| Chip load | 0.050 mm/tooth | Entered |
| Feed per revolution | 0.200 mm/rev | Calculated |
| Feed rate | 954.9 mm/min | Calculated |
Material removal rate
| Item | Value |
|---|
Geometric volume removed per minute only — not a force, power, torque, tool-life or safe condition claim.
Machine limits
| Limit | Entered | Calculated | Status |
|---|
This only compares figures — it does not clamp or recalculate any value, and staying below a limit is not a safety approval.
Formula used
RPM = (vc × 1000) ÷ (π × D)
RPM = (150.0 m/min × 1000) ÷ (π × 10.00 mm) = 4,775 RPM
Feed = fz × teeth × RPM
Feed = 0.050 mm/tooth × 4 × 4,775 RPM = 954.9 mm/min
Feed/rev = fz × teeth
Feed/rev = 0.050 mm/tooth × 4 = 0.200 mm/rev
Assumes a rotating milling/routing cutter at a fixed diameter, RPM, feed and engagement. Does not model radial chip thinning, runout, tool deflection, machine dynamics, coolant strategy, tool wear or material variability.
How to use this calculator
- Choose Metric or Imperial units, and the fixed operation scope, milling/routing.
- Choose what to calculate: RPM and feed rate (from a cutting speed and chip load you already have), or cutting speed and chip load (from an RPM and feed rate you already have).
- Enter the cutter diameter and the number of flutes (effective teeth).
- Enter the two remaining values for your chosen mode.
- Optionally add the axial depth and radial width of cut to see material removal rate, or add your machine's maximum RPM and feed rate to compare the calculated values against them.
- Review the calculation summary, the formula used, and any warnings shown.
How are milling speeds and feeds calculated?
Spindle speed comes from the cutting speed and cutter diameter, and feed rate comes from the chip load, the number of teeth and the spindle speed. This calculator always uses the direct formula for the values entered, on full-precision numbers, rather than chaining through a rounded intermediate result.
- vc = cutting speed (m/min, or SFM in imperial units)
- D = effective cutter diameter (mm, or inches in imperial units)
- Feed rate = chip load per tooth × number of teeth × RPM
- Feed per revolution = chip load per tooth × number of teeth
- Reverse: cutting speed = (π × D × RPM) ÷ 1,000; chip load = feed ÷ (RPM × teeth)
- MRR = axial depth of cut × radial width of cut × feed rate
Worked example, metric: a 10 mm diameter cutter at a cutting speed of 150 m/min needs RPM = (150 × 1,000) ÷ (π × 10) ≈ 4,774.6 RPM. With 4 flutes and a chip load of 0.05 mm/tooth, feed rate = 0.05 × 4 × 4,774.6 ≈ 954.9 mm/min.
Worked example, imperial: a 0.5 in diameter cutter at 500 SFM needs RPM = (500 × 12) ÷ (π × 0.5) ≈ 3,819.7 RPM. With 4 flutes and a chip load of 0.002 IPT, feed rate = 0.002 × 4 × 3,819.7 ≈ 30.6 IPM.
In reverse, entering a spindle speed and feed rate gives the cutting speed and chip load those values imply — useful for checking a program or a machine's actual running parameters against the tool manufacturer's application data.
Metric and imperial units used
| Quantity | Metric | Imperial | Exact conversion |
|---|---|---|---|
| Diameter / engagement | mm | in | 1 in = 25.4 mm |
| Cutting speed | m/min | SFM (surface feet per minute) | 1 SFM = 0.3048 m/min |
| Chip load (feed per tooth) | mm/tooth | IPT (inches per tooth) | 1 IPT = 25.4 mm/tooth |
| Feed rate | mm/min | IPM (inches per minute) | 1 IPM = 25.4 mm/min |
| Material removal rate | mm³/min (and cm³/min) | in³/min | 1 in³ = 16,387.064 mm³ |
Every calculation is normalised to millimetres, metres per minute and mm³/min internally, so switching units converts the figures already entered rather than reinterpreting the same number under a different unit.
What does this calculator assume, and what does it not do?
This calculator covers milling and routing with a single rotating cutter, at a fixed diameter, RPM, feed rate, tooth count and engagement. It does not model radial chip thinning at low radial engagement, tool runout, tool deflection, machine dynamics, coolant strategy, tool wear or material variability, and the optional material removal rate is a geometric volume-per-time figure only — it does not estimate cutting force, spindle power, torque or tool life.
It does not cover drilling, turning, tapping, thread milling, grinding, sawing, laser or EDM processes, and it does not simulate a machine, generate G-code, or draw on a tool or material database. Any warning it shows is a neutral, calculated callout — never a claim that a result is safe, optimal, suitable, manufacturer-approved or guaranteed. Always check the tool manufacturer's application data, your machine's actual limits, holder and tool condition, workholding, coolant strategy and your shop's procedures before machining.