CNC Feed Rate Calculator
Feed rate is the speed at which the cutting tool advances through the workpiece, measured in inches per minute (IPM) or mm per minute. It is calculated from three parameters: spindle speed (RPM), chip load per tooth (the thickness of material removed by each cutting edge per revolution), and the number of cutting flutes on the end mill. This is the industry-standard formula from Machinery's Handbook and cutting tool manufacturer engineering guides.
CNC feed rate formula
Feed rate (IPM) = RPM * Chip load (IPT) * Number of flutes
Feed rate (mm/min) = Feed rate (IPM) * 25.4
Source: Machinery's Handbook (Industrial Press) and standard cutting tool manufacturer engineering references. IPM = inches per minute; IPT = inches per tooth.
Typical chip loads by material and cutter diameter
- Aluminum, 1/4 in end mill: 0.001 to 0.003 IPT
- Aluminum, 1/2 in end mill: 0.002 to 0.005 IPT
- Mild steel, 1/4 in end mill: 0.0005 to 0.001 IPT
- Hard wood, 1/4 in end mill: 0.002 to 0.005 IPT
- MDF/plywood, 1/4 in upcut spiral: 0.003 to 0.008 IPT
- Always consult the tool manufacturer datasheet for your specific cutter and material.
CNC feed rate calculator: frequently asked questions
What is chip load in CNC machining?
Chip load (also called feed per tooth) is the thickness of material removed by each cutting edge in one revolution. It is measured in inches per tooth (IPT) or millimetres per tooth. Recommended chip loads are published by cutting tool manufacturers for each tool diameter and material combination.
What chip load should I use for aluminum?
Chip loads for aluminum depend on cutter diameter. A common guideline from Machinery's Handbook: for a 1/4 inch (6.35 mm) end mill in aluminum, start with 0.001 to 0.003 IPT. For a 1/2 inch (12.7 mm) end mill, use 0.002 to 0.005 IPT. Always refer to your tool manufacturer's chart.
How does the number of flutes affect feed rate?
More flutes increase the feed rate at the same chip load and RPM. A 4-flute cutter feeds twice as fast as a 2-flute cutter at the same RPM and chip load. However, more flutes also reduce chip clearance, so 2-flute cutters are preferred for aluminum and soft materials.
What is the relationship between feed rate and surface finish?
Lower chip loads produce smoother finishes. For finishing passes, reduce chip load to 50 to 75% of the roughing value. For slotting cuts, reduce chip load by 10 to 20% compared to peripheral milling due to chip re-cutting.
Should I use the calculated feed rate exactly?
The calculated feed rate is a starting point. In practice, start at 60 to 75% of calculated feed, listen for chatter, and increase gradually. Tool wear, machine rigidity, and workholding all affect the optimal rate.
Official sources
- Industrial Press: Machinery's Handbook (standard industry reference for cutting parameters).
- NIST: Manufacturing Systems Integration Division.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.