Wood Screw Size Chart: Gauge, Diameter, Pilot Hole

Wood screws are sized by gauge, a number from #0 up to #24 that sets the diameter of the shank, and by length in inches. #8 is the everyday cabinet and deck-board size, #10 and #12 are for heavier work, and #6 and smaller are for hinges and small hardware. The chart gives the shank diameter of each gauge from the USDA Wood Handbook (Table 8-9), the approximate root (core) diameter, the lead holes the Handbook tested with, and the pilot and clearance drills our screw and nail size calculator recommends for everyday work. A second table shows how much load a screw takes to pull out of fifteen common woods.

Wood screw size chart: gauge, diameter and pilot holes

Two kinds of pilot hole, and which to use

The chart gives two sets of pilot sizes because they answer different questions. The Handbook lead holes are the small holes used in the Forest Products Laboratory withdrawal tests: about 70% of the thread root in softwood and 90% in hardwood. They give the most grip, and they are what the withdrawal table below assumes. They also make a screw hard to drive by hand, and in dense hardwoods a small screw can snap before it is fully seated.

The shop pilot sizes are larger, at or just above the root diameter, and are what most woodworkers drill: the thread still cuts into solid wood, the screw drives smoothly, and brass or small steel screws survive. Use the shop sizes for cabinets, furniture and hardware. Go smaller, toward the Handbook size, in soft or low-density wood where grip matters more than ease of driving. In every case drill a clearance hole through the top piece, the size of the shank or slightly larger, so the threads bite only in the bottom piece and the screw pulls the two together.

Where the gauge numbers come from

The shank diameter of a numbered screw follows a simple rule: 0.060 in plus 0.013 in for each gauge number. The fourth column shows the rule; it matches the Handbook’s Table 8-9 to the thousandth of an inch for every gauge from #4 to #24. So a #8 screw is 0.060 + 8 x 0.013 = 0.164 in (4.17 mm), and a #10 is 0.190 in. This is the same series used for machine screws, which is why a #10 wood screw and a #10-24 machine screw have the same diameter (see the UNC and UNF thread chart).

Length and gauge go together

The Handbook’s withdrawal equation was established for the combinations of length and gauge below (Table 8-8). Outside these limits, it says, real withdrawal loads are likely to be lower than the equation predicts, for example because a long thin screw breaks before it pulls out. The same table is a sensible buying guide: a 1/2 in screw thicker than #6 or a 3 in screw thinner than #12 is unusual.

Withdrawal by wood species

For a wood screw in the side grain of dry wood, the Handbook’s equation for the ultimate withdrawal load is p = 15,700 G² D L, where G is the specific gravity, D the shank diameter and L the length of thread in the piece holding the point (in pounds and inches). The table gives pounds per inch of thread engagement. In end grain, expect about 75% of these figures. Type A tapping screws (sheet metal screws) hold about 5% to 16% more than wood screws of the same size, with the bigger gain in dense woods.

Worked example: #8 screws through 3/4 in stock

A #8 x 1-1/4 in screw through a 3/4 in board leaves 1/2 in in the piece below. Assuming the thread runs the full 1/2 in, in eastern white pine (G = 0.35) the equation gives 15,700 x 0.35² x 0.164 x 0.5 = 158 lb; in sugar maple (G = 0.63) it is 511 lb. Moving up to a 2 in screw puts 1-1/4 in into the pine and raises the figure to about 394 lb. Penetration is the cheapest strength there is, as long as the point stays inside the wood.

Compare a nail: in Douglas-fir a #8 screw (0.164 in) takes about 593 lb per inch to pull out, an 8d common nail (0.131 in) about 164 lb. That gap is why cabinets, drawer bottoms and anything pulled on are screwed, while nails are used in framing, where most loads push sideways on the fastener.

Driving tips from the Handbook

• Rub soap or wax on the threads in dense woods. The Handbook says lubricant makes driving easier and has little effect on the final withdrawal resistance.
• Never start a wood screw with a hammer. It tears the wood fibres and damages the threads, and seriously reduces the load the screw can carry.
• For side loads, the screw should go into the bottom piece at least seven times its shank diameter (about 1-1/8 in for a #8). Keep the top piece about half as thick as that penetration, end distance at least the thickness of the top piece, and edge distance at least half of it.
• In particleboard, drive with modest torque: the threads strip if you over-tighten, and a moderate setting torque gives nearly the full withdrawal strength.

Safety and structural use

The withdrawal table gives average loads at failure in laboratory tests. Allowable loads for design are much lower, and are set by the NDS and by screw makers for their own products. For decks, ledgers, guards, stairs and anything else that carries people, use the fasteners required by your local building code or specified by the connector or screw manufacturer, or consult a licensed engineer. Modern structural screws are rated by their makers and are not covered by this chart.

Frequently asked questions

What is the diameter of a #8 wood screw?

0.164 in (4.17 mm). The rule is 0.060 in + 0.013 in x gauge, so #6 is 0.138 in, #10 is 0.190 in and #12 is 0.216 in (Wood Handbook Table 8-9).

What size pilot hole for a #8 screw?

For everyday work, 7/64 in in softwood and 1/8 in in hardwood, with an 11/64 in clearance hole through the top board. For maximum grip in softwood the Handbook’s test lead hole is smaller, about 5/64 in.

What size pilot hole for a #10 screw?

1/8 in in softwood and 9/64 in in hardwood, with a 3/16 in clearance hole through the top piece.

Do screws hold better than nails?

In withdrawal, much better: in Douglas-fir a #8 screw needs about 593 lb per inch of thread to pull out, an 8d common nail about 164 lb per inch (Wood Handbook equations). Nails can be better for side loads in framing because they bend instead of snapping.

How much less do screws hold in end grain?

About 25% less: the Wood Handbook puts end-grain withdrawal at about 75% of side-grain withdrawal, and notes the results are erratic. Avoid splitting by drilling a pilot hole.

Sources and method

Shank diameters and gauge limits are copied from the Handbook tables (public domain). Root diameters, lead holes and withdrawal values are computed by us from the Handbook rules and equations.

1. USDA Forest Service, Forest Products Laboratory. Wood Handbook: Wood as an Engineering Material, General Technical Report FPL-GTR-190 (2010), chapter 8, Fastenings (D. R. Rammer). A US Government publication in the public domain. Tables 8-8 and 8-9; Equations 8-10 and 8-12; text on root diameter, lead holes, tapping screws, end grain, lubrication and lateral loads.
2. Specific gravity of each species: Wood Handbook FPL-GTR-190, Tables 5-3b and 5-5b (ovendry weight, volume at 12% moisture content), the same data as our wood species database.
3. Shop pilot and clearance drill sizes: the values used by our screw and nail size calculator, which follow common published woodworking charts.

More thread and fastener tools

• All thread and fastener charts
• UNC and UNF thread chart
• Metric thread pitch chart
• Tap drill chart (inch and metric)
• Clearance hole chart
• Nail size chart
• Wood screw size chart
• Lag screw pilot hole chart
• Bolt torque chart
• Wrench size chart
• Drill bit size chart
• Thread engagement chart
• Nail gun nail sizes by gauge
• Screw and nail size calculator
• Tap drill size calculator
• Clearance hole size calculator
• Tapped hole depth calculator

Last reviewed: 24 October 2026. How we build and check our data: methodology and corrections. Spotted an error? Please let us know.