Drill Bit Size Calculator
Match drill bit sizes to inch fractions, decimal equivalents, and screw gauges for woodworking and metalworking.
Drill Bit Size Calculator
Fraction
5/32"
Decimal
0.15625"
Millimeters
3.97 mm
Screw Size
#6
Complete Drill Bit Size Chart
| Fraction | Decimal | MM | Screw |
|---|---|---|---|
| 1/16" | 0.0625" | 1.59 | #0 |
| 3/32" | 0.09375" | 2.38 | #1 |
| 1/8" | 0.125" | 3.18 | #4 |
| 5/32" | 0.15625" | 3.97 | #6 |
| 3/16" | 0.1875" | 4.76 | #8 |
| 7/32" | 0.21875" | 5.56 | #10 |
| 1/4" | 0.25" | 6.35 | #12 |
| 5/16" | 0.3125" | 7.94 | 5/16 |
| 3/8" | 0.375" | 9.53 | 3/8 |
| 7/16" | 0.4375" | 11.11 | 7/16 |
| 1/2" | 0.5" | 12.7 | 1/2 |
What Is a Drill Bit Size Chart?
A drill bit size chartmaps fractional inch diameters to their decimal inch, millimeter, and screw gauge equivalents — an essential reference for selecting the right bit for pilot holes, clearance holes, countersinks, and tapping across wood, metal, and composite materials.
The Drill Bit Size Calculator finds the correct drill diameter for any screw gauge or bolt size. Enter a screw number or bolt diameter and it returns the recommended softwood pilot hole, hardwood pilot hole, and full shank clearance hole size in both fractional inches and millimeters.
Pilot Hole Size Formula
A pilot hole pre-drills the path for a screw, reducing splitting risk and driving torque. The correct pilot hole size depends on the wood species and the screw size:
For metric conversion: multiply fractional inches by 25.4 to get millimeters. Example: 5/32 in pilot hole = 0.15625 × 25.4 = 3.97 mm.
Complete Drill Bit Size Conversion Table
| Fraction (in) | Decimal (in) | Millimeters (mm) | Screw Gauge | Common Use |
|---|---|---|---|---|
| 1/16 in | 0.0625 | 1.59 | #0–#1 | Hinges, small hardware |
| 5/64 in | 0.0781 | 1.98 | #2 | Small cabinet screws |
| 3/32 in | 0.0937 | 2.38 | #3–#4 | Softwood pilot holes |
| 7/64 in | 0.1094 | 2.78 | #5–#6 | Hardwood pilot #6 |
| 1/8 in | 0.1250 | 3.18 | #7–#8 | Standard pilot softwood |
| 9/64 in | 0.1406 | 3.57 | #9 | Medium pilot holes |
| 5/32 in | 0.1563 | 3.97 | #10 | Deck screws, framing |
| 11/64 in | 0.1719 | 4.37 | #11–#12 | Heavy framing screws |
| 3/16 in | 0.1875 | 4.76 | #14 | Lag bolt pilot holes |
| 7/32 in | 0.2188 | 5.56 | #16 | Clearance #10 screw |
| 1/4 in | 0.2500 | 6.35 | #20 | Clearance 1/4 in bolt |
| 5/16 in | 0.3125 | 7.94 | 5/16 | Clearance 5/16 in bolt |
| 3/8 in | 0.3750 | 9.53 | 3/8 | Clearance 3/8 in bolt |
| 7/16 in | 0.4375 | 11.11 | 7/16 | Clearance 7/16 in bolt |
| 1/2 in | 0.5000 | 12.70 | 1/2 | Clearance 1/2 in bolt |
How to Choose the Right Drill Bit Size
For Wood Screws (Pilot Holes)
- Identify the screw gauge (#4, #6, #8, #10, #12, etc.).
- Determine wood species: softwood (pine, cedar) vs. hardwood (oak, maple).
- Select pilot hole size: for softwood use the smaller (core) diameter; for hardwood use the larger (shank) diameter.
- Drill a countersink if using flat-head screws to allow the head to sit flush.
For Clearance Holes
A clearance hole allows the screw shank to pass through freely without threading into the top board, so the fastener can draw the two pieces together under clamping pressure. The clearance hole diameter equals the shank outer diameter or slightly larger.