Drill Bit Conversion Chart
Convert drill bit sizes between millimeters, decimal inches, common fractions, and numbered drill bits. Use exact sizes for tap drilling and precision work; use the closest common equivalent only when a slight undersize or oversize is acceptable.
Quick Answer
To convert millimeters to inches, divide by 25.4. To convert inches to millimeters, multiply by 25.4. The chart below links to exact conversion pages for common sizes like 5 mm, 3/8 inch, #29, and #44 drill bits.
Popular Drill Bit Conversions
All Conversion Pages
| Size | Decimal Inches | Metric | Closest Common Option |
|---|---|---|---|
| 2 mm drill bit | 0.0787 in | 2.00 mm | 5/64 inch |
| 3 mm drill bit | 0.1181 in | 3.00 mm | #31 |
| 4 mm drill bit | 0.1575 in | 4.00 mm | 5/32 inch |
| 4.5 mm drill bit | 0.1772 in | 4.50 mm | #16 |
| 5 mm drill bit | 0.1969 in | 5.00 mm | #8 |
| 6 mm drill bit | 0.2362 in | 6.00 mm | 15/64 inch |
| 8 mm drill bit | 0.3150 in | 8.00 mm | 5/16 inch |
| 8.5 mm drill bit | 0.3346 in | 8.50 mm | Q |
| 10 mm drill bit | 0.3937 in | 10.00 mm | 25/64 inch |
| 10.5 mm drill bit | 0.4134 in | 10.50 mm | Z |
| 12 mm drill bit | 0.4724 in | 12.00 mm | 15/32 inch |
| 16 mm drill bit | 0.6299 in | 16.00 mm | 5/8 inch |
| 19 mm drill bit | 0.7480 in | 19.00 mm | 3/4 inch |
| 1/8 inch drill bit | 0.1250 in | 3.18 mm | 3 mm |
| 3/32 inch drill bit | 0.0938 in | 2.38 mm | 2.5 mm |
| 3/16 inch drill bit | 0.1875 in | 4.76 mm | 5 mm |
| 1/4 inch drill bit | 0.2500 in | 6.35 mm | 6 mm |
| 5/16 inch drill bit | 0.3125 in | 7.94 mm | 8 mm |
| 7/32 inch drill bit | 0.2188 in | 5.56 mm | 5.5 mm |
| 3/8 inch drill bit | 0.3750 in | 9.53 mm | 10 mm |
| 1/2 inch drill bit | 0.5000 in | 12.70 mm | 13 mm |
| 5/8 inch drill bit | 0.6250 in | 15.88 mm | 16 mm |
| 11/32 inch drill bit | 0.3438 in | 8.73 mm | 8.5 mm |
| #29 drill bit | 0.1360 in | 3.45 mm | 9/64 inch |
| #44 drill bit | 0.0860 in | 2.18 mm | 3/32 inch |
| #27 drill bit | 0.1440 in | 3.66 mm | 9/64 inch |
| #19 drill bit | 0.1660 in | 4.22 mm | 11/64 inch |
Drill Bit Conversion FAQ
How do I convert a metric drill bit to inches?
Divide the millimeter size by 25.4 to get decimal inches. For example, 5 mm divided by 25.4 equals 0.1969 inches. Then compare that decimal to fractional, numbered, or letter drill sizes to find the closest standard bit.
Are metric and fractional drill bits exact equivalents?
Usually no. Many metric and fractional drill bit sizes are close but not identical. Use the exact size when drilling for taps, dowels, tight clearance holes, or manufacturer-specified hardware.
What is the closest standard drill bit to 5 mm?
A 5 mm drill bit is 0.1969 inches. The closest numbered drill is #8 at 0.1990 inches, while common fractional choices are 13/64 inch for a slight oversize or 3/16 inch for a slight undersize.