When drilling and tapping a hole you need to drill your workpiece to the right size and in order to tap your workpiece to the correct size. Below is an SAE drill and tap chart on both coarse thread and fine thread. You can find a metric drill and tap chart here. You can also find an article on how to drill and tap a hole properly here.
COARSE THREAD
| TAP SIZE | DRILL SIZE | DECIMAL | MILLIMETERS |
|---|---|---|---|
| 1-64 | #53 | 0.0595 | 1.511 |
| 2-56 | #50 | 0.0700 | 1.778 |
| 3-48 | #47 | 0.0785 | 1.994 |
| 4-40 | #43 | 0.0890 | 2.261 |
| 5-40 | #38 | 0.1015 | 2.578 |
| 6-32 | #36 | 0.1065 | 2.705 |
| 8-32 | #29 | 0.1360 | 3.454 |
| 10-24 | #26 | 0.1470 | 3.734 |
| 12-24 | #16 | 0.1770 | 4.496 |
| 1/4-20 | #7 | 0.2010 | 5.105 |
| 5/16-18 | F | 0.2570 | 6.528 |
| 3/8-16 | 5/16 | 0.3125 | 7.938 |
| 7/16-14 | U | 0.3680 | 9.347 |
| 1/2-13 | 27/64 | 0.4219 | 10.716 |
| 9/16-12 | 31/64 | 0.4844 | 12.304 |
| 5/8-11 | 17/32 | 0.5312 | 13.492 |
| 3/4-10 | 21/32 | 0.6562 | 16.667 |
| 7/8-9 | 49/64 | 0.7656 | 19.446 |
| 1-8 | 7/8 | 0.8750 | 22.225 |
| 1 1/8-7 | 63/64 | 0.9844 | 25.004 |
| 1 1/4-7 | 1 7/64 | 1.1094 | 28.179 |
| 1 3/8-6 | 1 7/32 | 1.2187 | 30.955 |
| 1 1/2-6 | 1 11/32 | 1.3437 | 34.130 |
| 1 3/4 -5 | 1 9/16 | 1.5625 | 39.688 |
| 2-4 1/2 | 1 25/32 | 1.7812 | 45.242 |
FINE THREAD
| TAP SIZE | DRILL SIZE | DECIMAL | MILLIMETERS |
|---|---|---|---|
| 0-80 | 3/64 | 0.0469 | 1.191 |
| 1-72 | #53 | 0.0595 | 1.511 |
| 2-64 | #50 | 0.0700 | 1.778 |
| 3-56 | #46 | 0.0810 | 2.057 |
| 4-48 | #42 | 0.0953 | 2.375 |
| 5-44 | #37 | 0.1040 | 2.642 |
| 6-40 | #33 | 0.1130 | 2.870 |
| 8-36 | #29 | 0.1360 | 3.454 |
| 10-32 | #21 | 0.1590 | 4.039 |
| 12-28 | #15 | 0.1800 | 4.572 |
| 1/4-28 | #3 | 0.2130 | 5.410 |
| 5/16-24 | I | 0.2720 | 6.909 |
| 3/8-24 | Q | 0.3320 | 8.433 |
| 7/16-20 | 25/64 | 0.3906 | 9.921 |
| 1/2-20 | 29/64 | 0.4531 | 11.509 |
| 9/16-18 | 33/64 | 0.5156 | 13.096 |
| 5/8-18 | 37/64 | 0.5781 | 14.684 |
| 3/4-16 | 11/16 | 0.6875 | 17.463 |
| 7/8-14 | 13/16 | 0.8125 | 20.638 |
| 1-12 | 59/64 | 0.9219 | 23.416 |
| 1 1/8-12 | 1 3/64 | 1.0469 | 26.591 |
| 1 1/4-12 | 1 11/64 | 1.1719 | 29.766 |
| 1 3/8-12 | 1 19/64 | 1.2969 | 32.941 |
| 1 1/2-12 | 1 27/64 | 1.4219 | 36.116 |