Understanding Surface Speed Per Minute (SFM) in Grinding and Machining

SFM means surface feet per minute: the length of belt passing a point in one minute. MPH describes the same linear belt speed in miles per hour.

Convert belt-speed units

SFM = MPH × 88
MPH = SFM ÷ 88

Examples: 14 MPH = 1,232 SFM; 40 MPH = 3,520 SFM; 60 MPH = 5,280 SFM.

Calculate from your grinder

SFM = π × drive-wheel diameter in inches × actual motor RPM ÷ 12. See Calculating Belt Speed on Your 2x72 Grinder and the Belt Speed Calculator.

These conversions do not set operating limits. Use the approved speed range for the belt, wheel, attachment and task; small wheels can need substantially lower belt speed.