Screw Size Chart
Diameters and thread counts for numbered and fractional inch screws, wood screws, and metric screws. Measure a screw with the identifier below, or find the drill for its threads in the tap drill chart.
Identify a screw by its diameter
Measure across the outside of the threads with calipers.
Closest inch screw size
#10
0.190 in (4.83 mm) major diameter · 24 TPI coarse · 32 TPI fine. Use a thread gauge to tell coarse from fine.
Machine screw and bolt sizes (UNC / UNF)
| Size | Diameter (in) | Diameter (mm) | Coarse TPI (UNC) | Fine TPI (UNF) |
|---|---|---|---|---|
| #0 | 0.0600 | 1.52 | — | 80 |
| #1 | 0.0730 | 1.85 | 64 | 72 |
| #2 | 0.0860 | 2.18 | 56 | 64 |
| #3 | 0.0990 | 2.51 | 48 | 56 |
| #4 | 0.1120 | 2.84 | 40 | 48 |
| #5 | 0.1250 | 3.17 | 40 | 44 |
| #6 | 0.1380 | 3.51 | 32 | 40 |
| #8 | 0.1640 | 4.17 | 32 | 36 |
| #10 | 0.1900 | 4.83 | 24 | 32 |
| #12 | 0.2160 | 5.49 | 24 | 28 |
| 1/4" | 0.2500 | 6.35 | 20 | 28 |
| 5/16" | 0.3125 | 7.94 | 18 | 24 |
| 3/8" | 0.3750 | 9.52 | 16 | 24 |
| 7/16" | 0.4375 | 11.11 | 14 | 20 |
| 1/2" | 0.5000 | 12.70 | 13 | 20 |
| 9/16" | 0.5625 | 14.29 | 12 | 18 |
| 5/8" | 0.6250 | 15.88 | 11 | 18 |
| 3/4" | 0.7500 | 19.05 | 10 | 16 |
| 7/8" | 0.8750 | 22.22 | 9 | 14 |
| 1" | 1.0000 | 25.40 | 8 | 12 |
#0 only has a fine thread (#0-80).
Wood screw sizes
| Gauge | Diameter (in) | Diameter (mm) | Threads per inch |
|---|---|---|---|
| #2 | 0.086 | 2.18 | 26 |
| #3 | 0.099 | 2.51 | 24 |
| #4 | 0.112 | 2.84 | 22 |
| #5 | 0.125 | 3.17 | 20 |
| #6 | 0.138 | 3.51 | 18 |
| #7 | 0.151 | 3.84 | 16 |
| #8 | 0.164 | 4.17 | 15 |
| #9 | 0.177 | 4.50 | 14 |
| #10 | 0.190 | 4.83 | 13 |
| #12 | 0.216 | 5.49 | 11 |
| #14 | 0.242 | 6.15 | 10 |
| #16 | 0.268 | 6.81 | 9 |
Threads per inch are the ASME B18.6.1 values, allowed to vary ±10%.
Metric screw sizes
| Size | Diameter (mm) | Diameter (in) | Coarse pitch (mm) |
|---|---|---|---|
| M1.6 | 1.6 | 0.063 | 0.35 |
| M2 | 2 | 0.079 | 0.4 |
| M2.5 | 2.5 | 0.098 | 0.45 |
| M3 | 3 | 0.118 | 0.5 |
| M3.5 | 3.5 | 0.138 | 0.6 |
| M4 | 4 | 0.157 | 0.7 |
| M5 | 5 | 0.197 | 0.8 |
| M6 | 6 | 0.236 | 1 |
| M7 | 7 | 0.276 | 1 |
| M8 | 8 | 0.315 | 1.25 |
| M10 | 10 | 0.394 | 1.5 |
| M12 | 12 | 0.472 | 1.75 |
| M14 | 14 | 0.551 | 2 |
| M16 | 16 | 0.630 | 2 |
| M18 | 18 | 0.709 | 2.5 |
| M20 | 20 | 0.787 | 2.5 |
| M22 | 22 | 0.866 | 2.5 |
| M24 | 24 | 0.945 | 3 |
Screw Size Chart FAQ
What do screw numbers like #8 and #10 mean?
They are gauge numbers for screws smaller than 1/4 inch. The diameter in inches is 0.060 + 0.013 × the number, so a #8 is 0.164 in (4.17 mm) and a #10 is 0.190 in (4.83 mm). Wood screws use the same gauge diameters.
What does 10-24 or 1/4-20 mean?
The first number is the size (gauge or fraction of an inch) and the second is threads per inch. A 10-24 is a #10 screw with 24 threads per inch (coarse, UNC); a 10-32 is the same diameter with fine (UNF) threads.
How do I read a metric screw size like M6 × 1.0?
M6 means a 6 mm outside thread diameter, and 1.0 is the pitch: the distance between threads in millimeters. If the pitch is left off (just "M6"), it is the standard coarse pitch.
What size is a #8 wood screw?
A #8 wood screw has a 0.164 in (about 4.2 mm) basic diameter and about 15 threads per inch under ASME B18.6.1.
Sources
Machine screw diameters and threads per inch from the Unified Thread Standard (ASME B1.1), as tabulated in Wikipedia from Machinery's Handbook. Wood screw diameters and threads per inch from ASME B18.6.1 (CDE Fasteners spec sheet). Metric coarse pitches from ISO 261.