# Tap drill size calculator and inch tap drill chart

URL: https://www.clove3d.com/tools/tap-drill/

Tap drill sizes for UNC, UNF and metric threads, with the percent thread every drill cuts. Pick a thread and a target engagement to get the closest fractional, number, letter or metric drill.

## Formula

% thread = (D - d) / (1.299 x P) x 100
  inch:   % thread = TPI x (D - d) / 0.01299
  metric: % thread = 76.98 x (D - d) / P
drill for a target: d = D - (% / 100) x 1.299 x P
D = major diameter, d = drill diameter, P = pitch (same units)

## Inch tap drill chart (UNC / UNF, about 75% thread)

| Thread | Tap drill | in | mm | % thread |
|--------|-----------|----|----|----------|
| 4-40 UNC | #43 | 0.0890 | 2.26 | 71% |
| 6-32 UNC | #36 | 0.1065 | 2.71 | 78% |
| [8-32](https://www.clove3d.com/tools/tap-drill/8-32/) UNC | #29 | 0.1360 | 3.45 | 69% |
| 10-24 UNC | #25 | 0.1495 | 3.80 | 75% |
| [10-32](https://www.clove3d.com/tools/tap-drill/10-32/) UNF | #21 | 0.1590 | 4.04 | 76% |
| [1/4-20](https://www.clove3d.com/tools/tap-drill/1-4-20/) UNC | #7 | 0.2010 | 5.11 | 75% |
| 1/4-28 UNF | #3 | 0.2130 | 5.41 | 80% |
| [5/16-18](https://www.clove3d.com/tools/tap-drill/5-16-18/) UNC | F | 0.2570 | 6.53 | 77% |
| [3/8-16](https://www.clove3d.com/tools/tap-drill/3-8-16/) UNC | 5/16" | 0.3125 | 7.94 | 77% |
| 3/8-24 UNF | Q | 0.3320 | 8.43 | 79% |
| 1/2-13 UNC | 27/64" | 0.4219 | 10.72 | 78% |
| 1/2-20 UNF | 29/64" | 0.4531 | 11.51 | 72% |
| 5/8-11 UNC | 17/32" | 0.5313 | 13.49 | 79% |
| 3/4-10 UNC | 21/32" | 0.6563 | 16.67 | 72% |

Metric chart: https://www.clove3d.com/tools/tap-drill/metric/

## Guides

- Percent thread explained: https://www.clove3d.com/guides/percent-thread/
- Why 3D printed holes come out small: https://www.clove3d.com/guides/3d-printed-holes/

Standard drills are taken from published charts (Engineers Edge: machinist screw thread tap drill chart (ANSI); Penn MEDesign: tap drill chart; ETSU: tap, drill & clearance chart) and checked against the formula on every build.