Wood screw countersink size chart (free printable PDF)
The countersink drill diameter for every common wood screw, #4 to #14, in fractions and millimetres — so a flat head seats perfectly flush. Every size uses 82°, the US standard angle for flat-head wood screws. Download the free printable PDF or print it from the page.
Wood screw countersink size chart
| Screw gauge | Countersink diameter | Plug / bung |
|---|---|---|
| #4 | 1/4"6.4 mm | 1/4" |
| #6 | 5/16"7.9 mm | 5/16" |
| #8 | 3/8"9.5 mm | 3/8" |
| #10 | 7/16"11.1 mm | 1/2" |
| #12 | 1/2"12.7 mm | 1/2" |
| #14 | 1/2"12.7 mm | 1/2" |
Every size is 82° — the US standard included angle for flat-head wood screws — so a countersink bit matches all of them. #8 is highlighted (the most common wood screw). Plug / bung is the counterbore hole diameter if you sink the head deeper and cap it with a wooden plug — a separate job from countersinking flush.
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How to read it
Find your screw gauge on the left; the countersink diameter is the size of the cone-shaped recess that lets a flat-head screw sit flush. Match a 82° countersink bit to it — that angle is the US flat-head wood-screw standard and is the same for every gauge, so only the diameter changes with screw size. Drill the pilot hole first, then cut the countersink to depth.
These are wood-screw sizes, matched to flat-head wood-screw heads — not the ANSI machine-screw / socket-head countersinks, which share the gauge numbers but measure differently.
The angle: 82° (a constant)
You only need to get the diameter right — the angle is fixed. US flat-head wood screws are made to an 82° included angle, so a single 82° countersink (or a combination countersink-pilot bit) works across the whole #4–#14 range. Metric flat-head screws often use 90° instead, so if you’re driving metric hardware, match the bit to the screw.
New to countersinking, or unsure how deep to go? The full how-to covers the technique, depth, and countersink vs. counterbore.
How to countersink a screwCommon questions
What size countersink for a #8 wood screw?
For a #8 flat-head wood screw, use a 3/8" (9.5 mm) countersink — that matches the screw head so it seats flush. Countersinks for wood screws are cut at 82°, the US flat-head standard.
What angle is a wood screw countersink?
82°. Flat-head wood screws in the US use an 82° included angle, so a matching 82° countersink lets the head sit perfectly flush. (Many metric screws use 90° instead — match the bit to your screws.) The 82° applies to every gauge; only the diameter changes with screw size.
What's the difference between a countersink and a counterbore?
A countersink is an angled, cone-shaped recess that lets a flat-head screw sit flush with the surface. A counterbore is a straight-walled, flat-bottomed, deeper hole — used to sink the head below the surface so it can be capped with a wooden plug, or to seat a bolt head or washer. The 'plug / bung' column above is the counterbore size for plugging over the screw.
Do wood screw and machine screw countersinks use the same sizes?
No. Flat-head wood screws and machine / socket-head screws share the #4/#6/#8 gauge numbering but have different head sizes, so their countersinks differ. This chart is for wood screws — sized to flat-head wood-screw heads at 82°. Don't use machine-screw (ANSI 82°/100°) countersink dimensions for wood screws.
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Where these numbers come from
Countersink diameters cross-referenced from common woodworking sources; they match standard flat-head wood-screw head diameters at the 82° standard angle. Sources vary slightly at #12 (7/16"–1/2"); we list 1/2" so the head is sure to seat flush — err a hair larger rather than leave the head standing proud. These are wood-screw values, not machine / socket-head (ANSI) countersinks.
These are general woodworking guidance sizes for flat-head wood screws at 82°. Head sizes vary a little by manufacturer and screw style (bugle, flat, trim) — for a critical flush finish, test the countersink depth on a scrap of the same material first.