Metric drill bit size for wood
8 mm drill bit
The size of a 8 mm bit in both systems, how fast to run it on a drill press in softwood and hardwood for each kind of bit made in this size, and what it drills in the rest of this site’s charts.
Inch
0.315 in
8 mm ÷ 25.4; the nearest 64th is 5/16 in.
Metric
8 mm
The size as sold.
Drill press speed by bit type
RPM in softwood (pine) and hardwood (hard maple), on face grain. The figure is the median of three charts, or the mean of two, and the lower of two that are more than twice apart. Each chart’s own figure is listed under it. A dash means fewer than two charts cover that bit at this size.
| Bit | Softwood RPM | Hardwood RPM |
|---|---|---|
| Twist drill bit | 2,500 Only two sources publish this: WOOD Magazine and Grizzly WOOD Magazine 3,000 · Grizzly 2,000 | 1,500 Only two sources publish this: WOOD Magazine and Grizzly WOOD Magazine 1,500 · Grizzly 1,500 |
| Brad-point bit | 1,900 Only two sources publish this: WOOD Magazine and Grizzly WOOD Magazine 1,800 · Grizzly 2,000 | 1,125 Only two sources publish this: WOOD Magazine and Grizzly WOOD Magazine 750 · Grizzly 1,500 |
| Spade (paddle) bit | 2,000 Only two sources publish this: WOOD Magazine and Grizzly WOOD Magazine 2,000 · Grizzly 2,000 | 1,500 Only two sources publish this: WOOD Magazine and Grizzly WOOD Magazine 1,500 · Grizzly 1,500 |
| Forstner bit | 2,200 Only two sources publish this: WOOD Magazine and Grizzly WOOD Magazine 2,400 · Grizzly 2,000 | 700 Two sources disagree: WOOD Magazine 700, Grizzly 1500 WOOD Magazine 700 · Grizzly 1,500 |
Bigger bits and hole saws run slower: every chart here steps the speed down as the size grows.
Hardwood never runs faster than softwood with the same bit, and usually slower.
The charts are a starting point: when a bit or hole saw comes with its maker’s speed, use that.
One source: Grizzly, the maker of that drill press , sources [2]
WOOD Magazine tested on face grain: slow down when drilling into end grain.
One source: WOOD Magazine, the publisher of that chart , sources [1]
Clamp the work to the drill press table: a large bit at low speed can grab it.
Sources
- WOOD Magazine, WOOD Magazine’s Drill Press Speed Chart: twist, brad-point, spade bits and hole saws in softwood (pine) and hardwood (hard maple), read 2026-11-08
- Grizzly, G7943/G7944 drill press manual (mfd. since 09/17): drill bit speed chart, p. 27 (a guide; the bit maker’s speed comes first), read 2026-11-08
- Exchange-A-Blade, Hole saw tech: bimetal hole saw recommended RPM by size, wood column, read 2026-11-08
What this size drills on this site
This site’s pilot, clearance and dowel holes are given in inch sizes; the inch size above is this bit’s equivalent. The pilot hole chart and drill bit size chart have every size.
Sources, read 2026-11-07/08: WOOD Magazine, WOOD Magazine’s Drill Press Speed Chart: twist, brad-point, spade bits and hole saws in softwood (pine) and hardwood (hard maple); Grizzly, G7943/G7944 drill press manual (mfd. since 09/17): drill bit speed chart, p. 27 (a guide; the bit maker’s speed comes first); Exchange-A-Blade, Hole saw tech: bimetal hole saw recommended RPM by size, wood column; Infinity Cutting Tools, Forstner Bit Speed & Feed Chart (HSS Forstner bits, hardwoods and softwoods, 3/8" to 2").