Drilling Guide
How to Calculate Drill Speeds and Feeds
The two numbers that decide whether you get a clean hole and a long tool life, or a burnt workpiece and a broken bit.
Every drilling operation comes down to two settings: how fast the drill spins (spindle speed, in RPM) and how fast it advances into the material (feed rate). Get both right and you get clean chips, a good finish and a drill that lasts. Get either wrong and you're looking at burnt material, work-hardening, or a snapped bit.
Skip the maths
Enter your material, drill type and diameter to get RPM and feed rate instantly.
Spindle speed (RPM)
RPM comes from the material's recommended cutting speed and the drill diameter — bigger drills need to spin slower to hit the same surface speed at the cutting edge:
Typical cutting speeds (HSS drills)
| Material | Cutting speed |
|---|---|
| Mild steel | ≈25 m/min |
| Alloy steel | ≈15 m/min |
| Stainless steel | ≈12 m/min |
| Cast iron | ≈25 m/min |
| Aluminium | ≈80 m/min |
| Brass | ≈45 m/min |
These are HSS baseline figures — see drill bit types explained for how cobalt and carbide change the multiplier.
Feed rate
Feed rate is how fast the drill moves down the hole, set by RPM and the feed per revolution:
Feed per revolution scales with drill size — roughly 0.04mm/rev at 3mm, up to 0.10mm/rev at 6mm, 0.18mm/rev at 10mm, and 0.32mm/rev at 20mm. Too high a feed overloads and snaps the drill; too low causes rubbing, heat and work-hardening, especially in stainless.
Worked example: 6mm hole in mild steel, HSS drill
Step by step
- Cutting speed for mild steel, HSS: 25 m/min
- RPM = (25 × 1000) ÷ (π × 6) = ≈1,326 rpm
- Feed per rev at 6mm diameter: ≈0.10mm/rev
- Feed rate = 1,326 × 0.10 = ≈133 mm/min
If your machine can't hit the exact RPM, choose the nearest speed below it — running a little slow is safer than running too fast. Once you have the feed rate, see peck drilling explained for how to handle deeper holes, or head to the drill time tab to estimate total job time.
Frequently asked questions
How do I calculate drill RPM?
RPM = (cutting speed × 1000) ÷ (π × diameter), with cutting speed in m/min and diameter in mm. Cutting speed depends on material and drill type.
What cutting speed should I use for drilling steel?
For HSS: mild steel ≈25, alloy steel ≈15, stainless ≈12, cast iron ≈25, aluminium ≈80, brass ≈45 m/min. Cobalt runs ≈1.5× faster, carbide several times faster.
What feed per revolution should I use?
Roughly 0.04mm/rev at 3mm, up to 0.10mm/rev at 6mm, 0.18mm/rev at 10mm, and 0.32mm/rev at 20mm — scale with drill diameter.