Metric Tap Drill Bit Size Calculator
Use this calculator to estimate a drill diameter for standard and special metric taps.
Enter the major diameter and thread pitch in millimeters. The calculator identifies the closest drill size listed in the conversion chart below. For inch-thread taps, use our Special Tap and Drill Bit Size Calculator.
Metric Tap Drill Size Formula
Drill diameter (mm) = Major diameter (mm) − Thread pitch (mm)
Example: For an M11 × 2 tap, enter 11 mm for the major diameter and 2 mm for the pitch. The calculated drill size is 9.00mm. The calculator then suggests the closest listed drill size. This is an approximate starting point; verify suitability for the material and desired thread engagement.
How to Use This Calculator
- Enter the major diameter in millimeters, such as 11 for an M11 tap.
- Enter the metric thread pitch in millimeters (for example, 2 for M11 × 2).
- Read the calculated drill diameter, displayed in decimal mm.
- Review the suggested closest drill size, then verify that it is suitable for your application.
Drill Size Conversion Chart
The chart lists fractional, number, letter, and metric drill sizes alongside their decimal-inch equivalents. The original values are preserved, organized into three easier-to-read sections. A blank cell means that size designation does not apply to that entry.
Drill Size Reference — Part 1
| Fraction (in) | Decimal (in) | Number / Letter | Metric (mm) |
|---|---|---|---|
| — | 0.0098 | — | 0.25 |
| — | 0.0118 | — | 0.30 |
| — | 0.0135 | 80 | — |
| — | 0.0138 | — | 0.35 |
| — | 0.0145 | 79 | — |
| 1/64 | 0.0156 | — | — |
| — | 0.0157 | — | 0.40 |
| — | 0.0160 | 78 | — |
| — | 0.0177 | — | 0.45 |
| — | 0.0180 | 77 | — |
| — | 0.0197 | — | 0.50 |
| — | 0.0200 | 76 | — |
| — | 0.0210 | 75 | — |
| — | 0.0217 | — | 0.55 |
| — | 0.0225 | 74 | — |
| — | 0.0236 | — | 0.60 |
| — | 0.0240 | 73 | — |
| — | 0.0250 | 72 | — |
| — | 0.0256 | — | 0.65 |
| — | 0.0260 | 71 | — |
| — | 0.0276 | — | 0.70 |
| — | 0.0280 | 70 | — |
| — | 0.0292 | 69 | — |
| — | 0.0295 | — | 0.75 |
| — | 0.0310 | 68 | — |
| 1/32 | 0.0313 | — | — |
| — | 0.0315 | — | 0.80 |
| — | 0.0320 | 67 | — |
| — | 0.0330 | 66 | — |
| — | 0.0335 | — | 0.85 |
| — | 0.0350 | 65 | — |
| — | 0.0354 | — | 0.90 |
| — | 0.0360 | 64 | — |
| — | 0.0370 | 63 | — |
| — | 0.0374 | — | 0.95 |
| — | 0.0380 | 62 | — |
| — | 0.0390 | 61 | — |
| — | 0.0394 | — | 1.00 |
| — | 0.0400 | 60 | — |
| — | 0.0410 | 59 | — |
| — | 0.0420 | 58 | — |
| — | 0.0430 | 57 | — |
| — | 0.0433 | — | 1.10 |
| — | 0.0465 | 56 | — |
| 3/64 | 0.0469 | — | — |
| — | 0.0472 | — | 1.20 |
| — | 0.0512 | — | 1.30 |
| — | 0.0520 | 55 | — |
| — | 0.0550 | 54 | — |
| — | 0.0551 | — | 1.40 |
| — | 0.0591 | — | 1.50 |
| — | 0.0595 | 53 | — |
| 1/16 | 0.0625 | — | — |
| — | 0.0630 | — | 1.60 |
| — | 0.0635 | 52 | — |
| — | 0.0669 | — | 1.70 |
| — | 0.0670 | 51 | — |
| — | 0.0700 | 50 | — |
| — | 0.0709 | — | 1.80 |
| — | 0.0730 | 49 | — |
| — | 0.0748 | — | 1.90 |
| — | 0.0760 | 48 | — |
| 5/64 | 0.0781 | — | — |
| — | 0.0785 | 47 | — |
| — | 0.0787 | — | 2.00 |
| — | 0.0810 | 46 | — |
| — | 0.0820 | 45 | — |
| — | 0.0827 | — | 2.10 |
| — | 0.0860 | 44 | — |
| — | 0.0866 | — | 2.20 |
| — | 0.0890 | 43 | — |
| — | 0.0906 | — | 2.30 |
| — | 0.0935 | 42 | — |
| 3/32 | 0.0938 | — | — |
| — | 0.0945 | — | 2.40 |
| — | 0.0960 | 41 | — |
| — | 0.0980 | 40 | — |
| — | 0.0984 | — | 2.50 |
| — | 0.0995 | 39 | — |
| — | 0.1015 | 38 | — |
| — | 0.1024 | — | 2.60 |
| — | 0.1040 | 37 | — |
| — | 0.1063 | — | 2.70 |
| Fraction (in) | Decimal (in) | Wire (#) Letter (A-Z) | Metric (mm) |
Drill Size Reference — Part 2
| Fraction (in) | Decimal (in) | Number / Letter | Metric (mm) |
|---|---|---|---|
| — | 0.1065 | 36 | — |
| 7/64 | 0.1094 | — | — |
| — | 0.1100 | 35 | — |
| — | 0.1102 | — | 2.80 |
| — | 0.1110 | 34 | — |
| — | 0.1130 | 33 | — |
| — | 0.1142 | — | 2.90 |
| — | 0.1160 | 32 | — |
| — | 0.1181 | — | 3.00 |
| — | 0.1200 | 31 | — |
| 1/8 | 0.1250 | — | — |
| — | 0.1285 | 30 | — |
| — | 0.1360 | 29 | — |
| — | 0.1378 | — | 3.50 |
| — | 0.1405 | 28 | — |
| 9/64 | 0.1406 | — | — |
| — | 0.1440 | 27 | — |
| — | 0.1470 | 26 | — |
| — | 0.1495 | 25 | — |
| — | 0.1520 | 24 | — |
| — | 0.1540 | 23 | — |
| 5/32 | 0.1563 | — | — |
| — | 0.1570 | 22 | — |
| — | 0.1575 | — | 4.00 |
| — | 0.1590 | 21 | — |
| — | 0.1610 | 20 | — |
| — | 0.1660 | 19 | — |
| — | 0.1695 | 18 | — |
| 11/64 | 0.1719 | — | — |
| — | 0.1730 | 17 | — |
| — | 0.1770 | 16 | — |
| — | 0.1772 | — | 4.50 |
| — | 0.1800 | 15 | — |
| — | 0.1820 | 14 | — |
| — | 0.1850 | 13 | — |
| 3/16 | 0.1875 | — | — |
| — | 0.1890 | 12 | — |
| — | 0.1910 | 11 | — |
| — | 0.1935 | 10 | — |
| — | 0.1960 | 9 | — |
| — | 0.1968 | — | 5.00 |
| — | 0.1990 | 8 | — |
| — | 0.2010 | 7 | — |
| 13/64 | 0.2031 | — | — |
| — | 0.2040 | 6 | — |
| — | 0.2055 | 5 | — |
| — | 0.2090 | 4 | — |
| — | 0.2130 | 3 | — |
| — | 0.2165 | — | 5.50 |
| 7/32 | 0.2188 | — | — |
| — | 0.2210 | 2 | — |
| — | 0.2280 | 1 | — |
| — | 0.2340 | A | — |
| 15/64 | 0.2344 | — | — |
| — | 0.2362 | — | 6.00 |
| — | 0.2380 | B | — |
| — | 0.2420 | C | — |
| — | 0.2460 | D | — |
| 1/4 | 0.2500 | E | — |
| — | 0.2559 | — | 6.50 |
| — | 0.2570 | F | — |
| — | 0.2610 | G | — |
| 17/64 | 0.2656 | — | — |
| — | 0.2660 | H | — |
| — | 0.2720 | I | — |
| — | 0.2756 | — | 7.00 |
| — | 0.2770 | J | — |
| — | 0.2810 | K | — |
| 9/32 | 0.2813 | — | — |
| — | 0.2900 | L | — |
| — | 0.2950 | M | — |
| — | 0.2953 | — | 7.50 |
| 19/64 | 0.2969 | — | — |
| — | 0.3020 | N | — |
| 5/16 | 0.3125 | — | — |
| — | 0.3150 | — | 8.00 |
| — | 0.3160 | O | — |
| — | 0.3230 | P | — |
| 21/64 | 0.3281 | — | — |
| — | 0.3320 | Q | — |
| — | 0.3346 | — | 8.50 |
| — | 0.3390 | R | — |
| 11/32 | 0.3438 | — | — |
| Fraction (in) | Decimal (in) | Wire (#) Letter (A-Z) | Metric (mm) |
Drill Size Reference — Part 3
| Fraction (in) | Decimal (in) | Number / Letter | Metric (mm) |
|---|---|---|---|
| — | 0.3480 | S | — |
| — | 0.3543 | — | 9.00 |
| — | 0.3580 | T | — |
| 23/64 | 0.3594 | — | — |
| — | 0.3680 | U | — |
| — | 0.3740 | — | 9.50 |
| 3/8 | 0.3750 | — | — |
| — | 0.3770 | V | — |
| — | 0.3860 | W | — |
| 25/64 | 0.3906 | — | — |
| — | 0.3937 | — | 10.00 |
| — | 0.3970 | X | — |
| — | 0.4040 | Y | — |
| 13/32 | 0.4063 | — | — |
| — | 0.4130 | Z | — |
| — | 0.4134 | — | 10.50 |
| 27/64 | 0.4219 | — | — |
| — | 0.4331 | — | 11.00 |
| 7/16 | 0.4375 | — | — |
| — | 0.4528 | — | 11.50 |
| 29/64 | 0.4531 | — | — |
| 15/32 | 0.4688 | — | — |
| — | 0.4724 | — | 12.00 |
| 31/64 | 0.4844 | — | — |
| — | 0.4921 | — | 12.50 |
| 1/2 | 0.5000 | — | — |
| — | 0.5118 | — | 13.00 |
| 33/64 | 0.5156 | — | — |
| 17/32 | 0.5313 | — | — |
| — | 0.5315 | — | 13.50 |
| 35/64 | 0.5469 | — | — |
| — | 0.5512 | — | 14.00 |
| 9/16 | 0.5625 | — | — |
| — | 0.5709 | — | 14.50 |
| 37/64 | 0.5781 | — | — |
| — | 0.5905 | — | 15.00 |
| 19/32 | 0.5938 | — | — |
| 39/64 | 0.6094 | — | — |
| — | 0.6102 | — | 15.50 |
| 5/8 | 0.6250 | — | — |
| — | 0.6299 | — | 16.00 |
| 41/64 | 0.6406 | — | — |
| — | 0.6496 | — | 16.50 |
| 21/32 | 0.6563 | — | — |
| — | 0.6693 | — | 17.00 |
| 43/64 | 0.6719 | — | — |
| 11/16 | 0.6875 | — | — |
| — | 0.6890 | — | 17.50 |
| 45/64 | 0.7031 | — | — |
| — | 0.7087 | — | 18.00 |
| 23/32 | 0.7188 | — | — |
| — | 0.7283 | — | 18.50 |
| 47/64 | 0.7344 | — | — |
| — | 0.7480 | — | 19.00 |
| 3/4 | 0.7500 | — | — |
| 49/64 | 0.7656 | — | — |
| — | 0.7677 | — | 19.50 |
| 25/32 | 0.7813 | — | — |
| — | 0.7874 | — | 20.00 |
| 51/64 | 0.7969 | — | — |
| — | 0.8071 | — | 20.50 |
| 13/16 | 0.8125 | — | — |
| — | 0.8268 | — | 21.00 |
| 53/64 | 0.8281 | — | — |
| 27/32 | 0.8438 | — | — |
| — | 0.8465 | — | 21.50 |
| 55/64 | 0.8594 | — | — |
| — | 0.8661 | — | 22.00 |
| 7/8 | 0.8750 | — | — |
| — | 0.8858 | — | 22.50 |
| 57/64 | 0.8906 | — | — |
| — | 0.9055 | — | 23.00 |
| 29/32 | 0.9063 | — | — |
| 59/64 | 0.9219 | — | — |
| — | 0.9252 | — | 23.50 |
| 15/16 | 0.9375 | — | — |
| — | 0.9449 | — | 24.00 |
| 61/64 | 0.9531 | — | — |
| — | 0.9646 | — | 24.50 |
| 31/32 | 0.9688 | — | — |
| — | 0.9842 | — | 25.00 |
| 63/64 | 0.9844 | — | — |
| 1 | 1.0000 | — | — |
| Fraction (in) | Decimal (in) | Wire (#) Letter (A-Z) | Metric (mm) |
Frequently Asked Questions
Can I use this calculator for special or nonstandard metric taps?
Yes. Enter the metric major diameter and thread pitch in millimeters. The calculated diameter is a starting estimate; verify the appropriate drill with the tap manufacturer.
What does M11 × 2 mean?
M11 is the nominal major diameter of 11 mm, and 2 is the thread pitch in millimeters. The calculator gives 11 − 2 = 9 mm.
What formula does this metric tap drill calculator use?
The formula is drill diameter (mm) = major diameter (mm) − thread pitch (mm). Unlike inch-thread calculations, metric pitch is entered in millimeters, not threads per inch.
What if the calculated drill diameter is not a standard size?
The calculator recommends the closest diameter listed in the conversion chart and provides a link to search for that drill bit. Verify the selection for your material and thread requirements.
Does this calculator work for inch taps or pipe taps?
This tool is intended for straight metric threads. For inch-thread taps, use our Special Tap and Drill Bit Size Calculator. Pipe threads may require different sizing guidance.
Related resources: Tap and Drill Sizes | Hand Taps | Hand Tap and Drill Sets.