Turning Feed & Speed Calculator

Cutting speed and workpiece diameter give you spindle RPM, then feed per revolution gives you the feed rate to program — both in one pass.

Machine profile (optional) — what this does

Cutting speed (SFM)

Workpiece diameter (in)

Feed per revolution (in/rev)

Same RPM formula as milling, different feed logic

RPM = (SFM × 12) ÷ (π × diameter) works exactly the same way for turning as it does for any other operation — it's converting cutting speed and diameter into a spindle speed. Where turning differs is feed: a lathe tool feeds per spindle revolution (in/rev), not per tooth, so feed rate (IPM) = RPM × feed per revolution, with no flute count in the equation at all.

Diameter changes as the cut progresses

Unlike a milling cutter's fixed diameter, a turned workpiece's diameter shrinks as material comes off — the RPM calculated here is only correct for the diameter you entered. On a roughing pass taking a lot of stock off, recalculate for the new diameter partway through, or use your control's constant surface speed (CSS/G96) mode to have it adjust automatically.

Feed per revolution ranges to start from

Roughing generally runs feed in the 0.010–0.020 in/rev range in steel, finishing passes closer to 0.002–0.006 in/rev for a good surface finish — check the result against the Surface Finish Calculator if the pass is a finishing operation with a specific Ra target.