How to Calculate Chip Load, Speed and Feed
By Calvin Wu, Owner · Reviewed by Jacky Wrong · Last updated 2026-10-22
Spindle speed RPM = (Vc × 1000) ÷ (π × D). Feed rate = RPM × fz × Z. Chip load, or feed per tooth, is fz = feed rate ÷ (RPM × Z). Use Vc and fz from approved tool data for your material.
Key takeaways
- Vc is cutting speed (m/min or SFM); fz is feed per tooth (mm or inch).
- At light radial engagement the real chip is thinner than fz, so feed can be increased.
- These are starting estimates: verify before machining.
How do I calculate spindle speed?
RPM = (Vc × 1000) ÷ (π × D) with Vc in m/min and D in mm; imperial: RPM = (SFM × 12) ÷ (π × D in inches).
How do I calculate feed rate and chip load?
Feed rate = RPM × fz × Z. Rearranged, chip load fz = feed rate ÷ (RPM × Z).
Z is the number of flutes. Feed per tooth is the thickness of material each cutting edge removes per revolution.
Worked example
A 10 mm, 4-flute tool at Vc 100 m/min and fz 0.05 mm gives about 3,183 RPM and 637 mm/min.
RPM = 100 × 1000 ÷ (π × 10) = 3,183. Feed = 3,183 × 0.05 × 4 = 637 mm/min.
The numbers 100 m/min and 0.05 mm are arithmetic inputs for this example only, not a recommendation for any material.
What is radial chip thinning?
When radial engagement ae is below half the diameter, the actual chip thickness is smaller than fz, so feed per tooth can be raised to compensate.
Approximate maximum chip thickness for a straight-flute square end mill with ae ≤ D/2: h = fz × 2·√((ae/D)·(1 − ae/D)). It is a geometric approximation that ignores helix angle, runout and tool deflection, so treat the adjusted feed as a starting point. Example: at ae = 0.1·D, h ≈ 0.6 × fz.
FAQ
What is chip load?
Chip load, or feed per tooth (fz), is the thickness of material each cutting edge removes per revolution.
Are calculated values safe to use directly?
No. They are starting estimates; verify against tool data and machine capability before machining.