ConverterHub

Cutting Speed Calculator

Find the cutting speed for a machining operation.

How it is calculated

The tool computes Vc = π × D × N / 1000, where D is the tool or workpiece diameter in millimetres and N is the spindle speed in revolutions per minute. The result Vc is in metres per minute. It also converts that to feet per minute by multiplying by 3.28084.

Diameter must be greater than zero; RPM may be zero (giving 0.00) but not negative. Both results are rounded to two decimals. The tool gives the speed that your RPM produces; it does not know your material, so you compare the result with the recommended range for the tool and material yourself.

Worked example

A 12 mm end mill runs at 3000 rpm. Circumference: π × 12 = 37.70 mm per revolution. Multiply by 3000 rpm: 113,097 mm/min, and dividing by 1000 gives 113.10 m/min. In feet, 113.10 × 3.28084 = 371.05 ft/min. You would then check whether that figure sits inside the recommended band for your cutter and material.

Try this example →

Common mistakes

  • Entering the diameter in inches. The field is in millimetres, so a 0.5 in cutter is 12.7 mm.
  • Using the wrong diameter: for turning it is the workpiece diameter at the cut, which shrinks as you machine; for milling it is the cutter diameter.
  • Mixing up surface speed with feed rate. Vc is how fast the edge passes the material, not how fast the tool travels along it.
  • Entering feet per minute from an imperial chart as if it were m/min; check which unit the recommended value uses.
  • Forgetting the machine's maximum spindle speed: the calculated RPM for a small tool may be above what the spindle can deliver.

About this calculator

Cutting speed (also called surface speed, denoted Vc) is the speed at which a cutting tool's edge moves relative to the surface of the workpiece being machined, calculated as Vc = π · D · N / 1000, where D is the diameter (in mm) of the tool (for milling/drilling) or workpiece (for turning), N is the spindle speed in revolutions per minute (RPM), and the result is in meters per minute. It's essentially the tangential velocity of a point on the rotating diameter.

Machinists, CNC programmers and manufacturing engineers use cutting speed to select the correct spindle RPM for a given tool and material combination — every material and tool coating has a recommended cutting speed range (found in machinability tables) that balances tool life against material removal rate. Running too fast overheats and dulls the tool prematurely; running too slow wastes cycle time and can cause poor surface finish or built-up edge. This calculator finds Vc from diameter and RPM, or can be rearranged to find the RPM needed for a target cutting speed.

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