### Machining Speeds and Feeds Equations & Calculator

**Engineering Calculators | Engineering Metals and Materials**

**Machining Speeds and Feeds Equations Calculator**

Machining operations may be conducted on machine tools having a rotating spindle or a rotating part (lathe). Cutting speeds are usually given in feet or meters per minute and these speeds must be converted to spindle speeds, in revolutions per minute, to operate the machine. Conversion is accomplished by use of the following formulas:

Open machining Speeds and Feeds Calculator

*For Spindle velocity in rpm, the equation is:*

N = 12V / π D for inch units

and

N = 1000V / π D for metric units

Where:

N = Spindle speed in revolution per minute (rpm)

V = Cutting speed in feet per minute (fpm) or (meter per minute (m/min)

In turning operations, D is the diameter of the work piece; in milling, drilling, reaming, and other operations that use a rotating tool, D is the cutter diameter in inches for U.S. units and in millimeters for metric units. Reference π = 3.14159.

*Cutting speed in fpm or m/min, the equation is:*

V = πDN / 12 for inch units

and

V = πDN/1000 for metric units

Where:

N = Spindle speed in revolution per minute (rpm)

V = Cutting speed in feet per minute (fpm) or (meter per minute (m/min)

D = Cutter or work piece diameter