How to use the fraction to decimal chart
Find the fraction in the first column and read across for its decimal and its size in millimeters. The chart lists every 64th of an inch; the rows in bold are the sixteenths, the marks on a standard US tape measure. Fractions are in lowest terms, so 8/64 appears as 1/8 and 24/64 as 3/8.
Mixed numbers. Look up the fraction and add the whole inches. 4 3/8 is 4 + 0.375 = 4.375 inches. For millimeters, add 25.4 mm for each whole inch: 4 × 25.4 + 9.525 = 111.125 mm.
Improper fractions. Divide first, then look up the remainder. 35/8 is 4 with 3 left over, so 35/8 = 4 3/8 = 4.375.
The decimals are exact: every 64th of an inch ends within six decimal places. Millimeters are rounded to three places, a thousandth of a millimeter; the converter above gives more when you need it.
Fraction to decimal chart: 1/64 to 1 inch
| Fraction (in) | Decimal (in) | Millimeters |
|---|---|---|
| 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 | 6.350 |
| 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 | 12.700 |
| 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 | 19.050 |
| 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 | 25.400 |
Decimal to fraction in inches
Going the other way, most decimals do not land exactly on a fraction, so you round to the nearest one:
- Multiply the decimal part by the fraction you want: 16 for sixteenths, 32 or 64 for finer work.
- Round to the nearest whole number. That is the top of the fraction.
- Put it over 16 (or 32 or 64) and reduce.
For 2.7 inches: 0.7 × 16 = 11.2, which rounds to 11, so the answer is 2 11/16 inches (2.6875), 0.0125 inch short. The converter does this for you and shows the error at every precision.
In this chart the number in brackets is the fraction minus the decimal, in inches: + means the fraction is a little longer, − a little shorter.
| Decimal (in) | Nearest 1/16 | Nearest 1/32 | Nearest 1/64 |
|---|---|---|---|
| 0.05 | 1/16 (+0.0125) | 1/16 (+0.0125) | 3/64 (−0.0031) |
| 0.10 | 1/8 (+0.0250) | 3/32 (−0.0063) | 3/32 (−0.0063) |
| 0.15 | 1/8 (−0.0250) | 5/32 (+0.0063) | 5/32 (+0.0063) |
| 0.20 | 3/16 (−0.0125) | 3/16 (−0.0125) | 13/64 (+0.0031) |
| 0.25 | 1/4 (exact) | 1/4 (exact) | 1/4 (exact) |
| 0.30 | 5/16 (+0.0125) | 5/16 (+0.0125) | 19/64 (−0.0031) |
| 0.35 | 3/8 (+0.0250) | 11/32 (−0.0063) | 11/32 (−0.0063) |
| 0.40 | 3/8 (−0.0250) | 13/32 (+0.0063) | 13/32 (+0.0063) |
| 0.45 | 7/16 (−0.0125) | 7/16 (−0.0125) | 29/64 (+0.0031) |
| 0.50 | 1/2 (exact) | 1/2 (exact) | 1/2 (exact) |
| 0.55 | 9/16 (+0.0125) | 9/16 (+0.0125) | 35/64 (−0.0031) |
| 0.60 | 5/8 (+0.0250) | 19/32 (−0.0063) | 19/32 (−0.0063) |
| 0.65 | 5/8 (−0.0250) | 21/32 (+0.0063) | 21/32 (+0.0063) |
| 0.70 | 11/16 (−0.0125) | 11/16 (−0.0125) | 45/64 (+0.0031) |
| 0.75 | 3/4 (exact) | 3/4 (exact) | 3/4 (exact) |
| 0.80 | 13/16 (+0.0125) | 13/16 (+0.0125) | 51/64 (−0.0031) |
| 0.85 | 7/8 (+0.0250) | 27/32 (−0.0063) | 27/32 (−0.0063) |
| 0.90 | 7/8 (−0.0250) | 29/32 (+0.0063) | 29/32 (+0.0063) |
| 0.95 | 15/16 (−0.0125) | 15/16 (−0.0125) | 61/64 (+0.0031) |
Millimeters to inch fractions
One inch is exactly 25.4 mm, so a millimeter is 5/127 of an inch. The first whole number of millimeters that lands exactly on a 64th of an inch is 127 mm, which is 5 inches; everything smaller has to be rounded. Divide by 25.4 and round to the nearest fraction:
| Millimeters | Decimal (in) | Nearest 1/16 | Nearest 1/32 |
|---|---|---|---|
| 1 | 0.0394 | 1/16 (+0.0231) | 1/32 (−0.0081) |
| 2 | 0.0787 | 1/16 (−0.0162) | 3/32 (+0.0150) |
| 3 | 0.1181 | 1/8 (+0.0069) | 1/8 (+0.0069) |
| 4 | 0.1575 | 3/16 (+0.0300) | 5/32 (−0.0012) |
| 5 | 0.1969 | 3/16 (−0.0094) | 3/16 (−0.0094) |
| 6 | 0.2362 | 1/4 (+0.0138) | 1/4 (+0.0138) |
| 8 | 0.3150 | 5/16 (−0.0025) | 5/16 (−0.0025) |
| 10 | 0.3937 | 3/8 (−0.0187) | 13/32 (+0.0125) |
| 12 | 0.4724 | 1/2 (+0.0276) | 15/32 (−0.0037) |
| 15 | 0.5906 | 9/16 (−0.0281) | 19/32 (+0.0032) |
| 18 | 0.7087 | 11/16 (−0.0212) | 23/32 (+0.0101) |
| 19 | 0.7480 | 3/4 (+0.0020) | 3/4 (+0.0020) |
| 20 | 0.7874 | 13/16 (+0.0251) | 25/32 (−0.0062) |
| 25 | 0.9843 | 1 (+0.0157) | 31/32 (−0.0155) |
| 30 | 1.1811 | 1 3/16 (+0.0064) | 1 3/16 (+0.0064) |
| 50 | 1.9685 | 1 15/16 (−0.0310) | 1 31/32 (+0.0002) |
| 100 | 3.9370 | 3 15/16 (+0.0005) | 3 15/16 (+0.0005) |
The errors are in inches. 19 mm is within 0.002 inch of 3/4, close enough to treat as the same for most work; 12 mm is nearly 1/32 inch short of 1/2, enough to make a loose joint.
Which precision to use
- 1/16 inch is the finest mark on most tape measures and the usual precision for carpentry and most woodworking.
- 1/32 inch appears on many steel rules and some tapes, and is worth using for furniture and fine joinery.
- 1/64 inch is the step between sizes in a standard fractional drill bit set and the finest line on many machinist rules.
- Decimal inches are what calipers, machinists and CNC software use, usually to three places (a thousandth of an inch). To bring a caliper reading back to the tape, round it to the nearest 1/16 or 1/32 with the converter above.
Frequently asked questions
What is 4 3/8 as a decimal?
4.375. Keep the whole number and convert only the fraction. 3 ÷ 8 = 0.375, so 4 3/8 = 4 + 0.375 = 4.375 inches. In millimeters that is 111.125 mm.
What are 5 3/8 and 6 3/8 as decimals?
5.375 and 6.375. Any whole number plus 3/8 ends in .375, because 3/8 is 0.375. In millimeters, 5 3/8 inches is 136.525 mm and 6 3/8 inches is 161.925 mm.
How do you convert a fraction of an inch to a decimal?
Divide the top number by the bottom number. 5/16 is 5 ÷ 16 = 0.3125. For a mixed number such as 2 5/16, convert the fraction and add the whole inches to get 2.3125. Every fraction on a ruler or tape, down to 1/64, ends within six decimal places.
How do you convert decimal inches to a fraction?
Multiply the decimal part by 16 (or 32 or 64 for finer work), round to the nearest whole number, put it over 16 and reduce. For 0.43 inch, 0.43 × 16 = 6.88, which rounds to 7, so the nearest sixteenth is 7/16 inch (0.4375), 0.0075 inch longer.
What is 1/16 inch as a decimal and in millimeters?
1/16 inch is 0.0625 inch, or 1.5875 mm, a little over 1.5 mm. Twice that, 1/8 inch, is 0.125 inch (3.175 mm), and half of it, 1/32 inch, is 0.03125 inch (0.79375 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 fraction. 18 mm ÷ 25.4 = 0.7087 inch. The nearest 1/16 is 11/16 inch, about 0.02 inch short; the nearest 1/32 is 23/32 inch, about 0.01 inch long.
Last updated October 17, 2026.