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Gauge to specs
Type a wood screw gauge — the shank diameter and both pilot-hole bits appear below.
REFERENCE TABLE · EVERYDAY · HOME & GARAGE
Screw Sizes Chart
Every common screw size in one chart — wood screw gauges #2 through #14 with the shank diameter in decimal inches and millimeters plus the right pilot-hole drill bit for hardwood and softwood, and machine screws M3 through M10 with coarse pitch and tap-drill sizes. Three live lookups below: gauge to specs (a #6 is 0.138 inch / 3.5 mm), diameter to gauge (measured 0.164 inch? that’s a #8), and the pilot-hole finder (#8 in hardwood wants a 1/8-inch bit). The gauge math, the pilot-hole rule, and the drive-type guide are below the tables.
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Diameter to gauge
Measured the shank with calipers? Type the decimal inches — the nearest gauge appears below.
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Pilot-hole finder
Pick the gauge and the wood — the right drill bit appears below. Hardwood needs a bigger pilot than softwood.
The gauge math: one formula for every number
Wood screw gauges are not arbitrary — they follow a straight line: shank diameter = 0.060 + 0.013 × gauge. A #6 is 0.060 + 0.078 = 0.138 inch (3.5 mm); a #8 is 0.164 inch (4.2 mm); a #10 is 0.190 inch (4.8 mm). Bigger number, thicker shank, more holding power — and a bigger hole to drill first. Gauges #11 and #13 exist in the formula but are almost never manufactured, which is why the chart jumps from #10 to #12 to #14.
Wood screw gauges #2–#14
Decimal shank diameter, metric equivalent, and the pilot-hole drill bit for hardwood and softwood:
| Gauge | Shank diameter (in) | Diameter (mm) | Pilot hole · hardwood | Pilot hole · softwood |
|---|---|---|---|---|
| #2 | 0.086 | 2.2 | 1/16 (0.0625) | 1/32 (0.0313) |
| #3 | 0.099 | 2.5 | 5/64 (0.0781) | 1/16 (0.0625) |
| #4 | 0.112 | 2.8 | 5/64 (0.0781) | 1/16 (0.0625) |
| #5 | 0.125 | 3.2 | 3/32 (0.0938) | 5/64 (0.0781) |
| #6 | 0.138 | 3.5 | 7/64 (0.1094) | 3/32 (0.0938) |
| #7 | 0.151 | 3.8 | 1/8 (0.125) | 7/64 (0.1094) |
| #8 | 0.164 | 4.2 | 1/8 (0.125) | 7/64 (0.1094) |
| #9 | 0.177 | 4.5 | 9/64 (0.1406) | 1/8 (0.125) |
| #10 | 0.190 | 4.8 | 9/64 (0.1406) | 1/8 (0.125) |
| #12 | 0.216 | 5.5 | 5/32 (0.1563) | 9/64 (0.1406) |
| #14 | 0.242 | 6.1 | 11/64 (0.1719) | 5/32 (0.1563) |
Machine screws M3–M10
The M-number is the diameter in millimeters. Coarse pitch is the standard thread; the tap drill is what you drill before tapping the hole:
| Size | Diameter (mm) | Diameter (in) | Coarse pitch (mm) | Tap drill (mm) |
|---|---|---|---|---|
| M3 | 3 | 0.118 | 0.50 | 2.5 |
| M4 | 4 | 0.157 | 0.70 | 3.3 |
| M5 | 5 | 0.197 | 0.80 | 4.2 |
| M6 | 6 | 0.236 | 1.00 | 5.0 |
| M8 | 8 | 0.315 | 1.25 | 6.8 |
| M10 | 10 | 0.394 | 1.50 | 8.5 |
Worked example: hanging a shelf with #8 screws
You grab a box of #8 wood screws. The chart says the shank is 0.164 inch (4.2 mm) — the most common general-purpose screw in the drawer. You are driving into pine (softwood), so the pilot-hole finder gives you a 7/64-inch bit; if the shelf cleat were oak, it would give you 1/8 inch instead. Drill the pilot, drive the screw with a #2 Phillips or square bit, and the shelf holds — no split, no stripped hole.
Output · formula · meaning: how to read the chart
| Output | Formula | What it means |
|---|---|---|
| Shank diameter | 0.060 + 0.013 × gauge | #6 → 0.138 in (3.5 mm); #8 → 0.164 in (4.2 mm); #10 → 0.190 in (4.8 mm). |
| Nearest gauge | gauge with the smallest |ø measured − ø row| | Measured 0.164 in → #8. |
| Pilot-hole bit | ~85% of shank (hardwood) · ~70% (softwood), nearest bit | #8 in hardwood → 1/8 in; in softwood → 7/64 in. |
| Tap drill | diameter − pitch | M6×1.0 → 5.0 mm tap drill. |
Who uses this
- The weekend woodworker: the #6 that the plan calls for versus the #8s in the drawer — the chart says what actually fits the pilot hole.
- The furniture assembler: a bag of unmarked screws and a wobbly bookshelf — calipers plus the diameter lookup names the gauge.
- The 3D-print and electronics tinkerer: M3 heat-set inserts and M4 frame bolts — the machine table gives the tap drill in one glance.
- The first-time homeowner: hanging shelves, curtain rods, and TV mounts — the pilot-hole finder is the difference between solid and split.
Accuracy & limitations
Screw manufacturing tolerances are loose — a #8 from one brand can measure a few thousandths off from another, and cheap screws vary along the shank. Treat the chart as the nominal standard: if your calipers read 0.170, that is still a #8 (0.164 nominal), not a #9. Pilot-hole values assume a sharp twist bit and straight drilling; worn bits cut oversize, and end-grain or knots may want a slightly larger pilot. Machine-screw pitches are the ISO coarse standard — fine-thread variants (M6×0.75, M8×1.0) take different tap drills and are not covered here.
Cite this reference chartBright Side Kit. “Screw Sizes Chart.” brightoolbox.com, 2026.
Bright Side Kit. "Screw Sizes Chart." https://brightoolbox.com/screw-sizes-chart/ Accessed October 23, 2026.Frequently asked questions
What is the difference between screw gauge and metric sizes?
They are two different naming systems for the same thing: diameter. Wood screws use gauges (#2–#14), where the diameter follows the formula 0.060 + 0.013 × gauge — a #8 is 0.164 inch. Machine screws use metric (M3–M10), where the number is the diameter in millimeters — an M6 is 6 mm. The gauge lookup above converts any gauge to decimal inches and mm in one step.
What size pilot hole should I drill?
The rule of thumb: ~85% of the shank diameter for hardwood, ~70% for softwood — then round to the nearest standard bit. That gives a #8 a 1/8-inch pilot in hardwood and a 7/64-inch pilot in softwood; a #6 gets 7/64 in hardwood and 3/32 in softwood. Hardwood splits if the pilot is too small; softwood strips if it is too big. The pilot-hole finder picks the bit for your gauge and wood.
Why do screws have different drive types — Phillips, square, Torx?
Because the drive is where screws fail. Phillips (#2 fits most wood screws) is universal but cams out under torque; square/Robertson grips far better and dominates in construction; Torx/star handles the highest torque and rules deck screws. Match the bit to the screw head exactly — a #2 Phillips in a #3 recess is how stripped heads happen — and keep the driver straight and pressed in.
Why are there no #7, #9, #11, or #13 screws at the store?
#7 and #9 exist but are rarely stocked; #11 and #13 are almost never manufactured even though the gauge formula covers them. The retail ladder runs #6, #8, #10, #12, #14 because those five cover every practical jump in holding power. If a plan calls for a #9, a #8 or #10 from the chart above will do the job.
What is the difference between a wood screw and a machine screw?
The thread and the job. Wood screws have coarse, deep, tapered threads that bite into wood fibers — they cut their own path (after your pilot hole). Machine screws have uniform threads meant for a pre-tapped hole or a nut, sized in metric (M3–M10), and they are what hold electronics, machinery, and 3D-printer frames together. Never drive a machine screw into wood expecting it to hold — and never expect a wood screw to thread into a tapped metal hole.
What size tap drill do I need for an M6 screw?
5.0 mm — the rule is tap drill = diameter − pitch, and the standard M6 coarse pitch is 1.0 mm, so 6 − 1 = 5.0. From the chart: M3 → 2.5 mm, M4 → 3.3 mm, M5 → 4.2 mm, M8 → 6.8 mm, M10 → 8.5 mm. Those are coarse-thread values; fine-thread screws take different drills.
What happens if I skip the pilot hole?
In hardwood: the wood splits — the screw is a wedge, and oak or maple near an edge will crack audibly. In softwood near an edge: same, just quieter. In the middle of a pine board with a small screw, you will usually get away with it — until you don’t. The pilot hole takes ten seconds; the split board takes a trip to the store. When in doubt, drill it.