Choosing the correct drill bit is one of the most overlooked steps in fastening — the wrong size leads to stripped screws, split wood, or anchors that don't hold. This drill bit size guide and chart for screws covers pilot holes for wood screws, clearance holes, sheet metal screws, drywall anchors, and concrete fasteners so you can get it right every time.
How Do I Choose the Right Size Drill Bit for a Screw?
The rule depends on what type of hole you're drilling:
- Pilot hole in wood: The pilot hole for wood screws should be slightly smaller than the thread diameter. For softwood, use a drill bit slightly smaller than the root diameter of the screw — the threads need wood fiber to bite into. For hardwood, use a drill bit slightly smaller than the root diameter but closer to it — denser fiber means less compression, so the hole needs to be a bit larger than in softwood to avoid splitting.
- Clearance hole: A clearance hole must be larger than screw diameter — the screw shank passes through freely without threading into the first board. This is used in the top board of a two-board fastening where you want all the thread engagement in the second board.
- Sheet metal: The pilot hole for sheet metal screws should be small enough for threads to cut into the metal. Too large a hole and the self-tapping thread has nothing to cut.
If no chart is available, hold drill bits behind the screw to check size — the bit should disappear behind the solid shank diameter when held against the screw shaft (for pilot holes) or match the outer diameter (for clearance holes).
Standard Wood Screw Pilot Hole Chart
| Screw Size | Screw Diameter | Pilot Hole (Softwood) | Pilot Hole (Hardwood) | Clearance Hole |
|---|---|---|---|---|
| #2 | 0.086" | #56 (0.0465") | #54 (0.055") | #44 (0.086") |
| #4 | 0.112" | 5/64" or #47 | 7/64" | 7/64" |
| #6 | 0.138" | 7/64" or #35 | #29 (0.136") | 9/64" |
| #8 | 0.164" | #29 (0.136") | #18 (0.169") | 11/64" |
| #10 | 0.190" | 0.159" (#21) | #10 (0.193") | 3/16" |
| #12 | 0.216" | 3/16" | #2 (0.221") | 7/32" |
| #14 | 0.242" | 7/32" | 15/64" | 1/4" |
| 1/4" | 0.250" | 3/16" or #13 | 13/64" | 17/64" |
What Size Drill Bit to Drill Out a Screw?
To drill out a stuck or stripped screw completely, use a drill bit slightly larger than the screw's outer thread diameter — large enough to remove all the threads from the wood.
- For a #8 screw (0.164" diameter), a 3/16" drill bit (0.1875") removes the screw material cleanly.
- For a #10 screw, use a 13/64" or 7/32" bit.
After drilling out, you can use a larger fastener, fill the hole with a wooden toothpick and glue before re-driving, or relocate the fastener slightly.
What Size Hole to Drill for Screws in Metal?
Sheet metal screws are self-tapping and cut their own threads. The pilot hole needs to be just large enough for the screw's root diameter — the threads cut into the metal as they advance. Too small a hole snaps the screw; too large a hole produces no thread engagement.
| Sheet Metal Screw Size | Pilot Hole (Light Gauge) | Pilot Hole (Heavy Gauge) |
|---|---|---|
| #6 | #36 | #28 |
| #8 | #30 | #19 |
| #10 | #21 | #9 |
| #12 | #16 | #2 |
| #14 | #7 | D |
Drill Bit Sizing for Drywall Anchors
Drill bits for drywall anchors should fit snugly around the anchor. The anchor body needs the wall material to grip it — if the hole is too large, the anchor spins instead of setting. Choose a drill bit size close to but slightly smaller than the drywall anchor width. Most plastic expansion anchors specify the correct bit size on their packaging — follow it exactly. If in doubt, drill one size smaller than the anchor diameter and test the fit before drilling all your holes.
Understanding Drill Bit Sizing Systems
Drill bits come in three sizing systems that overlap across the full range:
- Fractional sizes (1/64", 1/32", 1/16", etc.) — Drill bit sizes include fractions of 64ths as the standard increment. This is the most common system for general hardware store bits.
- Number sizes (#1 through #80) — drill bits come in sizes from #80 to #1. Smaller numbers indicate a larger diameter in the letter/number system. #80 is the smallest (0.0135") and #1 is larger (0.228").
- Letter sizes (A through Z) — sizes over 0.2280" are named by letters A to Z. Letter A is just above #1 in the number series, and Z is the largest letter-series size at 0.413".
For most screw pilot hole work, fractional bits are the easiest to source. For precision drilling matching specific screw sizes, number-series bits are more precisely matched to the fractional screw diameter specifications.
Important note: Number sizes for drill bits are different from screw numbering. Screw numbering in the imperial system increases with diameter, so a smaller number indicates a smaller diameter. For example, a #8 screw (0.164” major diameter) is smaller than a #10 screw (0.190” major diameter).
Quick-Reference Tips
- For wood screws, drill bit should be slightly smaller the minor (root) diameter, not the outer thread diameter.
- A clearance hole must be larger than screw major diameter so the shank passes freely.
- For sheet metal, match the drill bit to the root diameter of self-tapping metal screws.
- Pre-drilling is recommended if installing closer than 1" from the edge of wood.
- Always test pilot holes in scrap before drilling the actual workpiece.
The right drill bit is just as important as the right screw. Taking the time to find the right size will help prevent loose connections and broken screws.