Drill RPM & Feed Calculator

Converts a cutting diameter and a surface speed into a spindle setting, then a chip load and flute count into a feed rate.

Formula

Shop charts write the inch form as RPM = 3.82 × SFM ÷ Ø. 3.82 is 12 ÷ π rounded to three figures; this page uses 12 ÷ π exactly and rounds only the displayed answer, so it lands a few rpm off the chart on large diameters. That difference is the chart's, not ours.

Assumptions

• Surface speed is your input, not our recommendation. Published SFM for a given material and tool disagrees by a factor of two or more between Machinery's Handbook, tooling catalogs, and shop practice, and it moves with coating, coolant, rigidity, and depth. BenchReference does not publish a number it cannot trace to one source, so this page asks you for it.
• Chip load is per tooth, per revolution. A twist drill has two cutting edges, so the feed per revolution is twice the chip load.
• The result is the speed at the cutting diameter. Step drills, spot drills, and countersinks run at their largest engaged diameter, not their nominal size.
• Peck depth, coolant, and thrust are not modeled.

Worked example

A 1/4″ (6.35 mm) drill at 100 SFM: 100 × 12 × 25.4 ÷ (π × 6.35) = 1528 rpm. At 0.05 mm per tooth on two flutes, the feed is 1528 × 0.05 × 2 = 153 mm/min (6.0 in/min).

Related

• Drill size chart — every diameter this page accepts
• Nearest drill finder — identify a measured bit
• All calculators