You can type 3.4375 or 3 7/16, or switch to millimeters and type 87.3. In the Off by column, a plus means the tape mark's a little longer than your size and a minus means it's shorter. Rounding goes to the nearest mark, and a size exactly halfway between two marks goes up.
The chart: every 64th of an inch
Sixteenths are in bold, because that's what most tapes are marked in. Thirty seconds are in color. Every decimal here is exact, since a 64th of an inch is 0.015625. The millimeters are rounded to three places, using the exact 25.4 mm to the inch.
| Fraction | Decimal | mm |
|---|---|---|
| 1/64″ | 0.015625 | 0.397 |
| 1/32″ | 0.03125 | 0.794 |
| 3/64″ | 0.046875 | 1.191 |
| 1/16″ | 0.0625 | 1.588 |
| 5/64″ | 0.078125 | 1.984 |
| 3/32″ | 0.09375 | 2.381 |
| 7/64″ | 0.109375 | 2.778 |
| 1/8″ | 0.125 | 3.175 |
| 9/64″ | 0.140625 | 3.572 |
| 5/32″ | 0.15625 | 3.969 |
| 11/64″ | 0.171875 | 4.366 |
| 3/16″ | 0.1875 | 4.763 |
| 13/64″ | 0.203125 | 5.159 |
| 7/32″ | 0.21875 | 5.556 |
| 15/64″ | 0.234375 | 5.953 |
| 1/4″ | 0.25 | 6.35 |
| 17/64″ | 0.265625 | 6.747 |
| 9/32″ | 0.28125 | 7.144 |
| 19/64″ | 0.296875 | 7.541 |
| 5/16″ | 0.3125 | 7.938 |
| 21/64″ | 0.328125 | 8.334 |
| 11/32″ | 0.34375 | 8.731 |
| 23/64″ | 0.359375 | 9.128 |
| 3/8″ | 0.375 | 9.525 |
| 25/64″ | 0.390625 | 9.922 |
| 13/32″ | 0.40625 | 10.319 |
| 27/64″ | 0.421875 | 10.716 |
| 7/16″ | 0.4375 | 11.113 |
| 29/64″ | 0.453125 | 11.509 |
| 15/32″ | 0.46875 | 11.906 |
| 31/64″ | 0.484375 | 12.303 |
| 1/2″ | 0.5 | 12.7 |
| Fraction | Decimal | mm |
|---|---|---|
| 33/64″ | 0.515625 | 13.097 |
| 17/32″ | 0.53125 | 13.494 |
| 35/64″ | 0.546875 | 13.891 |
| 9/16″ | 0.5625 | 14.288 |
| 37/64″ | 0.578125 | 14.684 |
| 19/32″ | 0.59375 | 15.081 |
| 39/64″ | 0.609375 | 15.478 |
| 5/8″ | 0.625 | 15.875 |
| 41/64″ | 0.640625 | 16.272 |
| 21/32″ | 0.65625 | 16.669 |
| 43/64″ | 0.671875 | 17.066 |
| 11/16″ | 0.6875 | 17.463 |
| 45/64″ | 0.703125 | 17.859 |
| 23/32″ | 0.71875 | 18.256 |
| 47/64″ | 0.734375 | 18.653 |
| 3/4″ | 0.75 | 19.05 |
| 49/64″ | 0.765625 | 19.447 |
| 25/32″ | 0.78125 | 19.844 |
| 51/64″ | 0.796875 | 20.241 |
| 13/16″ | 0.8125 | 20.638 |
| 53/64″ | 0.828125 | 21.034 |
| 27/32″ | 0.84375 | 21.431 |
| 55/64″ | 0.859375 | 21.828 |
| 7/8″ | 0.875 | 22.225 |
| 57/64″ | 0.890625 | 22.622 |
| 29/32″ | 0.90625 | 23.019 |
| 59/64″ | 0.921875 | 23.416 |
| 15/16″ | 0.9375 | 23.813 |
| 61/64″ | 0.953125 | 24.209 |
| 31/32″ | 0.96875 | 24.606 |
| 63/64″ | 0.984375 | 25.003 |
| 1″ | 1 | 25.4 |
Reading the chart
Find the decimal part of your size in the middle column and read the fraction on the left. If your size isn't there, it falls between two marks, and you'll need to pick the closer one. That's what the converter does for you.
Some worked examples, each rounded to 16ths:
- 3.4375″ is 3 7/16″ exactly, so there's nothing to round.
- 2.3″ rounds to 2 5/16″ on a tape marked in 16ths, which is 0.0125″ too long, about 0.32 mm.
- 75 mm (2.9528″) rounds to 2 15/16″ on a tape marked in 16ths, which is 0.0153″ too short, about 0.39 mm.
- 7.714″ rounds to 7 11/16″ on a tape marked in 16ths, which is 0.0265″ too short, about 0.67 mm.
The last one matters more than it looks. If you cut five pieces at that size and round each one, the error adds up five times. Cut from a running total instead, or round only at the end.
On the tape
An inch on a tape is split in half, then in quarters, eighths and sixteenths, and each level has a shorter line. The longest line inside the inch is the half, and it's easy to spot. The two next longest are the quarters, then the eighths, then the short sixteenth marks between them. To read 7/16, count seven of the smallest marks past the inch, or find 3/8 (that's 6/16) and go one mark further.
Fractions on a tape are always written as small as they'll go. 8/16 is written 1/2, 4/16 is 1/4, and 6/16 is 3/8. Only the odd sixteenths, 1/16, 3/16, 5/16 and so on, keep the 16 underneath. To practice on a drawn tape, try the tape measure trainer.
Which precision should you use?
- 1/8 inch is plenty for framing and rough work.
- 1/16 inch is what most tapes show and most trim work uses.
- 1/32 and 1/64 are for fine woodworking, machining and drill bit sizes, where a steel rule or calipers come out.
The worst a mark can be off is half its own size: 1/32 inch when you round to 16ths, about 0.79 mm. Rounding to 64ths cuts that to about 0.2 mm.
Questions
What is 0.375 inches as a fraction?
3/8 inch, exactly. In the chart it's 24/64, which reduces to 3/8.
How many millimeters is 1/16 inch?
1.5875 mm exactly, since an inch is 25.4 mm. Most people round it to 1.6 mm.
How do I convert millimeters to a fraction of an inch?
Divide by 25.4 to get decimal inches, then round to the nearest mark. The converter above does both steps when you pick millimeters.
Can I print the chart?
Yes. Print the chart puts all 64 rows on one page, in two columns. Choose Save as PDF in the print window to keep a file.
Is there a calculator that keeps fractions?
Yes. My Construction Calculator for Android adds, subtracts and divides feet, inches and fractions without rounding between steps, and rounds the answer to the mark you choose, from 1/2 down to 1/64 inch.
Construction Calculator
Feet, inches and fractions with exact math, rounded to the mark you choose.