A hole saw cuts at a surface speed, not at whatever the trigger happens to be. Enter the cup diameter and a starting SFM for the material. This returns RPM = (SFM × 3.82) / diameter in inches. Live, in the browser. Starting speed only — not a rating on the saw, the arbor, or the drill.
A hole saw cuts at a surface speed, not at whatever the trigger happens to be.
Use it when cutting holes with a hole saw in wood, steel, stainless or plastic in a drill press or a variable-speed drill. Pick the cup size and the material; the page converts a recommended surface speed into RPM. Large saws need much slower speeds than most people expect, and in metal a steady feed and cutting fluid matter as much as the dial.
Surface feet per minute is how fast a tooth travels around the cup. RPM is just that speed turned into spindle turns. The shop form uses the constant 3.82, which is 12/π rounded:
RPM = (SFM × 3.82) / D
D = hole-saw diameter in inches. 3.82 ≈ 12/π.
Exact: RPM = (SFM × 12) / (π D). Metric diameter: convert mm ÷ 25.4 first.
The number is a starting speed. It is not the max RPM stamped on a saw, not a cordless-drill rating, and not a substitute for the card that came with your bi-metal cup. If the cut smokes, chatters, or glazes the teeth, slow down and ease off the feed. Use cutting oil on steel. Wood and most plastics run dry.
Metal columns on public bi-metal hole-saw RPM cards are nearly the same number in SFM, just restated by diameter. Back-solving Lenox’s recommended-RPM table and Milwaukee Hole Dozer spec sheets (1 in cup: 350 mild steel, 175 stainless, 525 aluminum; 1-1/8 in Hole Dozer: 300 / 150 / 450) gives:
| Material | This calculator | Implied from the cards | Notes |
|---|---|---|---|
| Wood | 350 (band 300–500) | Cards list much higher RPM | Conservative start. A 2-1/4 in cup at 2000 RPM on a Starrett-style / Diamond Saw Works bi-metal card is ~1180 SFM — an upper operating figure, not a hand-drill start. |
| Mild steel | 90 (band 80–100) | ~92 SFM (1 in @ 350 RPM) | Matches Lenox / Milwaukee metal columns. Cutting oil. |
| Stainless | 45 (band 30–50) | ~46 SFM (1 in @ 175 RPM) | Same cards. Slow, firm feed, oil. Do not polish the work-harden. |
| Aluminum | 135 card / 250 machining | ~137 SFM (1 in @ 525 RPM) | Hole-saw cards sit ~135. Generic HSS machining charts often quote 200–300. Two presets; type anything. |
| Cast iron | 60 | ~62 SFM (1 in @ 235 RPM) | Same cards. Usually cut dry. |
Those SFM values are starting recommendations drawn from published hole-saw RPM cards and ordinary HSS machining bands. They are not a Lenox, Milwaukee, or Starrett manufacturer specification, not a max rating, and not a warranty number. Read the chart on the saw you bought if it disagrees.
| Case | Arithmetic | RPM |
|---|---|---|
| 2.25 in wood @ 350 SFM | (350 × 3.82) / 2.25 | 594 |
| 1 in mild steel @ 90 SFM | (90 × 3.82) / 1 | 344 |
| 1 in stainless @ 45 SFM | (45 × 3.82) / 1 | 172 |
| 1 in aluminum @ 135 SFM | (135 × 3.82) / 1 | 516 |
| 2.25 in mild steel @ 90 SFM | (90 × 3.82) / 2.25 | 153 |
| 57.15 mm wood @ 350 SFM | same 2.25 in cup | 594 |
The shop check is a 2-1/4 in hole saw in wood at 350 SFM: 1337 / 2.25 = 594.22, shown as 594 RPM. An independent check using the same 3.82 constant matches this page. Lenox’s 1 in mild-steel card number is 350 RPM, which is 92 SFM — this calculator’s 90 SFM start prints 344 RPM, a hair under the card, on purpose.
Start from surface speed, not a random dial number. Larger diameters want lower RPM so the rim teeth stay near a workable SFM; a 2 in saw at the same RPM as a ¾ in pilot is already spinning the rim much faster. If the saw smokes early or the arbor screams, drop speed before you lean harder.
Pilot the hole, then let the saw’s rim cut — forcing the feed packs chips in the cup and overheats the teeth. Back the saw out to clear chips on deep holes, especially in steel. Bi-metal cups tolerate intermittent contact better than cheap carbon cups; still treat the calculator’s RPM as a starting band, not a warranty.
Units: Diameter in inches, SFM in feet per minute, RPM as rev/min. Convert metric diameters before you type.
This page is a speed estimate from diameter and target SFM. It is not a tool-life model, not a coolant schedule, and not permission to ignore the cup’s stamped max RPM.
As a start, yes: (350 × 3.82) / 2.25 ≈ 594. That is the low end of a sensible wood band (300–500 SFM). Some bi-metal operating-speed cards list 2000 RPM for a 2-1/4 in cup in wood. That is roughly 1180 SFM — an upper figure for a sharp cup in a drill press, not a first pull on a cordless drill. Start around 600, listen, and only climb if the teeth are cutting clean chips without burning.
Those cards are RPM at a fixed implied SFM for each material. This page lets you pick the SFM, then solves RPM. For mild steel the cards imply about 90–92 SFM; for stainless about 45; for aluminum about 135. Dial those presets and a 1 in cup lands within a few RPM of the published 350 / 175 / 525 figures. Wood is the outlier: the cards run much faster than a conservative 350 SFM start.
Hole-saw RPM cards (Lenox recommended-RPM table, Milwaukee Hole Dozer spec sheets) sit near 135 SFM. Ordinary HSS machining charts often quote 200–300 SFM for aluminum. The 135 preset follows the hole-saw card. The 250 preset is the machining-band start. If the slug smears or the cup loads, drop SFM. If it is cutting cool with a light chip, you can climb. Type any number; both presets are starting guesses.
Steel and stainless: yes. Stainless in particular work-hardens if you spin too fast and rub. Cast iron is usually cut dry. Aluminum likes a little WD-40 or kerosene so the cup does not load. Wood and most plastics: dry, and clear chips. Oil does not change the RPM math; it keeps the teeth alive at that speed.
Treat the number as a gear/trigger target. A 1/2 in hole saw in wood can live in high gear. A 2-1/4 in cup in mild steel at ~150 RPM is low gear, slow trigger, two hands on the arbor if you have them. When in doubt, start slower than the calculator and feed so the teeth bite rather than polish. A drill press with a speed chart is the honest way to hit the number.
Use the unit stamped on the saw. US bi-metal cups are inch fractions (2-1/8 lockset, 2-1/4, 3, 4). Metric cups are millimetres. The formula always converts to inches because SFM is feet per minute. Switching units converts the diameter already typed. SFM does not convert — it is the same physical speed.
No. It is a starting cutting speed from SFM and diameter. It does not know your saw’s tooth form, cobalt percent, carbide vs bi-metal, arbor, drill, or how hard the work is clamped. It will happily print a number your cordless drill cannot reach, or a number that is still too fast for a dull cup in stainless. Not a manufacturer rating, not a structural spec, not a substitute for the chart in the box.