Wood Screw Size Chart: Gauge, Length & Pilot Hole Reference
You’re building a cabinet box, a bookshelf, or a workbench — and you need to choose between a #6, #8, or #10 screw in three different lengths. The gauge system isn’t intuitive (higher number = bigger diameter), and pilot hole sizing isn’t on the box. This chart gives you the complete reference: diameter conversions, length rules for common stock thicknesses, and pilot hole sizes for both softwood and hardwood.
Wood Screw Gauge: Diameter Chart
US wood screws use a gauge number system where each increment equals approximately 0.013 inches of shank diameter. The formula: diameter = (gauge × 0.013) + 0.060 inches. Memorize this and you can back-calculate any gauge on the fly.
Wood screw anatomy — flat countersink head, smooth shank near head, tapered threaded body, sharp self-starting tip. Length is always measured from the bottom of the head to the tip.
The most common gauges for woodworking are #4 through #12. Here is the complete diameter reference for those sizes:
| Gauge | Diameter (inches) | Diameter (mm) | Typical Use |
|---|---|---|---|
| #2 | 0.086" | 2.18 mm | Hobby models, small hinges, thin trim |
| #4 | 0.112" | 2.84 mm | Drawer slides, screen frames, small hardware |
| #6 | 0.138" | 3.51 mm | Cabinet face frames, hinges, trim, 1/2" stock |
| #8 | 0.164" | 4.17 mm | Most common — cabinet boxes, furniture, shelving, 3/4" stock |
| #10 | 0.190" | 4.83 mm | Heavy shelves, workbenches, thick hardwood joinery |
| #12 | 0.216" | 5.49 mm | Structural wood connections, heavy hardware mounting |
| #14 | 0.242" | 6.15 mm | Near the lag bolt territory — ledger boards, heavy brackets |
Don’t Know Your Screw Size?
Measure the shank diameter with calipers, then run it through our free identifier — it returns the exact designation in seconds.
Open Identifier →Wood Screw Length Chart by Material Thickness
The core rule: the screw should penetrate the receiving board by at least half its length, and ideally 2/3 of the total screw length should be in the receiving board. A shorter screw splits the load across too few threads; a longer screw punches through the back face.
| Top Board Thickness | Common Material | Recommended Screw | Penetration in Substrate |
|---|---|---|---|
| 1/4" | Drawer bottoms, cabinet backs | #6 × 3/4" | ~1/2" into substrate |
| 1/2" | Plywood, MDF panels | #8 × 1-1/4" | ~3/4" into substrate |
| 3/4" | Cabinet box sides, shelves, furniture | #8 × 1-1/4" to 1-1/2" | 1/2"–3/4" — use 1-1/2" in hardwood |
| 1" | Solid wood furniture, 5/4 lumber | #8 × 1-3/4" to 2" | 3/4"–1" into substrate |
| 1-1/2" | 2× lumber (actual 1-1/2"), thick slabs | #10 × 2-1/2" to 3" | 1"–1-1/2" into substrate |
| 2"+ | Workbench tops, laminated stock | #10 × 3" or lag bolt | Consider lag bolt for highest load |
Pilot Hole Sizes for Wood Screws
A pilot hole serves two purposes: it prevents the wood from splitting (especially near edges and in hardwood), and it guides the screw straight. The pilot hole diameter should match the thread root diameter — the screw's threads cut into the surrounding wood, but the core doesn’t need to displace material.
When you want two boards to draw tight together (the joinery scenario), drill two different holes: a clearance hole through the top board (matches the full shank diameter so the screw slides freely) and a pilot hole in the receiving board (smaller than the shank so the threads bite). Without the clearance hole, the screw grips both boards and the joint never fully closes.
Two-board joinery: the clearance hole through the top board (11/64" for #8) lets the screw slide freely. The pilot hole in the bottom board (3/32" for #8 in hardwood) gives the threads something to bite into. Without the clearance hole, the joint never closes fully.
| Gauge | Shank Dia. | Pilot — Softwood | Pilot — Hardwood | Clearance Hole |
|---|---|---|---|---|
| #4 | 0.112" | 3/64" (0.047") | 1/16" (0.063") | 7/64" (0.109") |
| #6 | 0.138" | 1/16" (0.063") | 5/64" (0.078") | 9/64" (0.141") |
| #8 | 0.164" | 5/64" (0.078") | 3/32" (0.094") | 11/64" (0.172") |
| #10 | 0.190" | 3/32" (0.094") | 7/64" (0.109") | 3/16" (0.188") |
| #12 | 0.216" | 7/64" (0.109") | 1/8" (0.125") | 7/32" (0.219") |
Wood Screw Head Types
The most common head type for woodworking is the flat countersink — it sits flush with or slightly below the surface after driving and can be filled with wood putty or a plug for a clean finish. The alternatives have specific use cases:
- Flat countersink — flush mount, standard for furniture, cabinets, and face frames. Requires a countersink bit to avoid a proud dimple.
- Round head — sits above the surface. Used when you want the screw visible or for holding thin material (sheet metal, hardware) against wood without pulling through.
- Pan head — low profile, sits above the surface. Common for woodworking jig hardware, adjustable shelving pins, and face-mount hinges.
- Oval / trim head — a hybrid of flat and round. Half of the head recesses into a countersink, the other half remains visible with a decorative domed profile. Used for finish hardware where appearance matters.
- Bugle head — like a flat head with a curved undercut. Designed to dimple into drywall and soft wood without tearing fibers. The bugle profile self-pilots without a countersink bit, which is why drywall screws don’t need pre-drilling into the paper.
Thread Type: Coarse vs Fine
Most wood screws use coarse thread. Coarse thread has a wider pitch (fewer threads per inch) which grips wood grain more aggressively and resists pull-out better than fine thread. The tapered thread form on a classic wood screw — where thread diameter increases from tip to shank — also acts as a wedge, drawing the threads tight into the surrounding wood fiber.
Fine-thread wood screws exist but are niche: they’re used in dense hardwoods where coarse threads would shear off during installation. In standard pine, poplar, or plywood, reach for coarse thread every time.
Partially threaded screws (threaded on the tip half, smooth shank near the head) are worth noting: they’re designed for long fastening runs where the smooth shank section acts like a built-in clearance hole. In practice, a fully threaded screw plus a separate clearance hole gives better control, but partially threaded screws are a convenient shortcut for simple butt joints.
Material Selection: When Coating Matters
| Coating | Use Case | Don’t Use When… |
|---|---|---|
| Zinc-plated (bright) | Dry interior furniture, cabinets, shelving | Any outdoor or moisture exposure — will rust |
| Phosphate / black oxide | Drywall, interior framing | Structural joinery — brittle, snaps under shear |
| Epoxy coated (yellow) | Interior cabinetry, IKEA-style flat-pack | Pressure-treated lumber — not rated for ACQ |
| Stainless 304 | Outdoor furniture, coastal/humid environments | Marine environments — use 316 stainless instead |
| Stainless 316 | Marine, coastal, saltwater exposure | High cost for typical non-marine use |
| Hot-dip galvanized (HDG) | Pressure-treated lumber, ground contact | Fine finish work — coating is rough and visible |
Quick Selection Cheat Sheet
If you’re standing in front of the hardware aisle and need the answer now:
- Drawer bottom (1/4") to cabinet side (3/4"): #6 × 1" or #8 × 1-1/4" — zinc-plated, flat head, pilot with 1/16" then 9/64" clearance.
- Cabinet box assembly (3/4" plywood): #8 × 1-5/8" coarse, zinc-plated — the standard Kreg-style pocket hole spec.
- Face frame joinery (hardwood, 3/4"): #8 × 1-1/4", pilot at 3/32", clearance at 11/64".
- Workbench top (1-1/2" lumber laminate): #10 × 3" or 5/16" hex bolts with barrel nuts — lag bolt territory if load is serious.
- Outdoor furniture, cedar or redwood: #8 × 1-1/2" stainless 304, pre-drill all of it.
- Pressure-treated deck rail posts: #10 × 3" HDG or structural screws rated for ACQ — never standard zinc.
Recommended Tool
Digital Caliper — 6" / 150mm
If you have an unknown screw and need the gauge, a $15–25 digital caliper measures the shank diameter in seconds. Cross-reference against the chart above to get the exact designation. The Neiko 6" model is the standard shop recommendation.
View on Amazon →Frequently Asked Questions
What size wood screw should I use for 3/4" material?
For joining 3/4" stock (the most common furniture and cabinet case material), use #8 × 1-1/4" or #8 × 1-1/2". The 1-1/4" length gives about 1/2" of thread penetration into the receiving board; the 1-1/2" gives 3/4", which is more secure for heavy shelves or hardwood joinery.
What pilot hole do I drill for a #8 wood screw?
For a #8 screw (0.164" shank): 5/64" in softwood, 3/32" in hardwood. For the top board in a two-piece joint, drill a 11/64" clearance hole so the threads don’t grip the top board — this is what lets the joint close fully.
What is the difference between a #6 and #8 wood screw?
#6 has a 0.138" (3.51mm) shank; #8 is 0.164" (4.17mm). #6 is standard for lighter work — hinges, cabinet hardware, thin trim. #8 is the workhorse for box construction and furniture. The shear strength difference is roughly 40%, which matters when the joint is loaded in tension or under weight.
Do I need to drill a pilot hole for wood screws?
In softwood (pine, poplar, cedar): optional for screws under #8 if you’re mid-board. In hardwood (oak, maple, walnut): always. Within 2" of any edge or end-grain: always, regardless of wood species. Skip the pilot hole and you’re gambling on a split — it’s not worth it on a finished piece.
What screw size is best for 1/2" plywood?
For 1/2" plywood: #6 × 1" or #8 × 1-1/4". The #8 × 1-1/4" is typically better — more holding power and less risk of backing out under load. Plywood has inconsistent internal layers, so deeper penetration compensates for voids in the substrate.