17.78 mm
Workshop reference
Fraction to Decimal Chart
Every 1/64 inch from 1/64 to 1 inch as a decimal and in millimeters, with the 1/16 steps marked. Below the chart is a converter that turns any decimal inch or mm into the nearest 1/16, 1/32 and 1/64 and shows how far off each one is.
The short answer
Divide the top of the fraction by the bottom. 5/8 is 0.625 in, which is 15.875 mm. Multiply inches by 25.4 for mm. Going the other way, multiply a decimal by 64, round to a whole number and reduce: 0.7 x 64 = 44.8, so 45/64.
Quick answers
The conversions people look up most, worked out from the chart below.
What is 5/8 as a decimal?
0.625 in, which is 15.875 mm.
What is 3/16 as a decimal?
0.1875 in, which is 4.7625 mm.
What are 1/4, 1/2 and 3/4 inch in mm?
6.35 mm, 12.7 mm and 19.05 mm.
What is 1 mm in inches?
0.0394 in. That is a little more than 1/32 in (0.794 mm) and a little less than 3/64 in (1.191 mm).
How do you turn a decimal into a fraction?
Multiply by 64, round to a whole number, then reduce. 0.7 x 64 = 44.8, so 45/64 (0.703125 in).
What is 10 mm as a fraction?
10 mm is 0.3937 in. The nearest 1/64 is 25/64 (0.390625 in), 0.0031 in under.
Fraction to decimal chart, 1/64 to 1 inch
All 64 steps in one chart that reads three ways. Go from the left column to the middle for a fraction to decimal chart, from the left to the right for a fraction to mm chart, and from the middle back to the left for a decimal to fraction chart. The 1/16 steps are highlighted.
1/64 to 1/2 inch
| Fraction | Decimal (in) | Millimeters |
|---|---|---|
| 1/64 | 0.015625 | 0.397 |
| 1/32 | 0.0313 | 0.794 |
| 3/64 | 0.046875 | 1.191 |
| 1/16 | 0.0625 | 1.588 |
| 5/64 | 0.078125 | 1.984 |
| 3/32 | 0.0938 | 2.381 |
| 7/64 | 0.109375 | 2.778 |
| 1/8 | 0.1250 | 3.175 |
| 9/64 | 0.140625 | 3.572 |
| 5/32 | 0.1563 | 3.969 |
| 11/64 | 0.171875 | 4.366 |
| 3/16 | 0.1875 | 4.763 |
| 13/64 | 0.203125 | 5.159 |
| 7/32 | 0.2188 | 5.556 |
| 15/64 | 0.234375 | 5.953 |
| 1/4 | 0.2500 | 6.350 |
| 17/64 | 0.265625 | 6.747 |
| 9/32 | 0.2813 | 7.144 |
| 19/64 | 0.296875 | 7.541 |
| 5/16 | 0.3125 | 7.938 |
| 21/64 | 0.328125 | 8.334 |
| 11/32 | 0.3438 | 8.731 |
| 23/64 | 0.359375 | 9.128 |
| 3/8 | 0.3750 | 9.525 |
| 25/64 | 0.390625 | 9.922 |
| 13/32 | 0.4063 | 10.319 |
| 27/64 | 0.421875 | 10.716 |
| 7/16 | 0.4375 | 11.113 |
| 29/64 | 0.453125 | 11.509 |
| 15/32 | 0.4688 | 11.906 |
| 31/64 | 0.484375 | 12.303 |
| 1/2 | 0.5000 | 12.700 |
33/64 to 1 inch
| Fraction | Decimal (in) | Millimeters |
|---|---|---|
| 33/64 | 0.515625 | 13.097 |
| 17/32 | 0.5313 | 13.494 |
| 35/64 | 0.546875 | 13.891 |
| 9/16 | 0.5625 | 14.288 |
| 37/64 | 0.578125 | 14.684 |
| 19/32 | 0.5938 | 15.081 |
| 39/64 | 0.609375 | 15.478 |
| 5/8 | 0.6250 | 15.875 |
| 41/64 | 0.640625 | 16.272 |
| 21/32 | 0.6563 | 16.669 |
| 43/64 | 0.671875 | 17.066 |
| 11/16 | 0.6875 | 17.463 |
| 45/64 | 0.703125 | 17.859 |
| 23/32 | 0.7188 | 18.256 |
| 47/64 | 0.734375 | 18.653 |
| 3/4 | 0.7500 | 19.050 |
| 49/64 | 0.765625 | 19.447 |
| 25/32 | 0.7813 | 19.844 |
| 51/64 | 0.796875 | 20.241 |
| 13/16 | 0.8125 | 20.638 |
| 53/64 | 0.828125 | 21.034 |
| 27/32 | 0.8438 | 21.431 |
| 55/64 | 0.859375 | 21.828 |
| 7/8 | 0.8750 | 22.225 |
| 57/64 | 0.890625 | 22.622 |
| 29/32 | 0.9063 | 23.019 |
| 59/64 | 0.921875 | 23.416 |
| 15/16 | 0.9375 | 23.813 |
| 61/64 | 0.953125 | 24.209 |
| 31/32 | 0.9688 | 24.606 |
| 63/64 | 0.984375 | 25.003 |
| 1 | 1.0000 | 25.400 |
Every decimal is exact. The 64ths are shown in full to six places and the other rows to four, so 1/32 reads 0.0313 here when it is exactly 0.03125. Millimeters come from exactly 25.4 mm to the inch, rounded to three places. For drill, bolt and thread sizes, see the drill size chart, the bolt and screw size chart and the tap drill chart.
Decimal to fraction converter
Type a decimal inch, a fraction or a size in mm. You get the nearest 1/16, 1/32 and 1/64, each with its decimal, its mm and how far off it is.
Decimal or mm to the nearest fraction
The nearest 1/16, 1/32 and 1/64
| Nearest | Fraction | Inches | mm | Off by |
|---|---|---|---|---|
| 1/16 | 11/16 | 0.6875 | 17.463 | 0.0125 in under |
| 1/32 | 11/16 | 0.6875 | 17.463 | 0.0125 in under |
| 1/64 | 45/64 | 0.703125 | 17.859 | 0.0031 in over |
Over means the fraction is bigger than your size and under means it is smaller. For a hole a bolt has to pass through, take a fraction that is over. For a part that has to fit into a hole, take one that is under.
How do you convert fractions and decimals?
Four conversions cover all of it. Inches are always 25.4 mm, so the mm ones are one multiply or divide.
Fraction to decimal
Divide the top number by the bottom one. 5/8 is 5 divided by 8, which is 0.625. 3/16 is 3 divided by 16, which is 0.1875.
Decimal to fraction
Multiply the decimal by 64 and round to a whole number, then reduce by halving the top and bottom while both are even. 0.7 x 64 = 44.8, which rounds to 45, so 45/64. Use 16 instead of 64 for a coarser fraction: 0.7 x 16 = 11.2, so 11/16 (0.6875 in, 0.0125 in under).
Fraction to mm
Turn the fraction into a decimal, then multiply by 25.4. 5/8 is 0.625 in, and 0.625 x 25.4 = 15.875 mm.
mm to fraction
Divide the mm by 25.4, then treat the answer as a decimal. 10 mm is 0.3937 in, which is 25.2 sixty-fourths, so 25/64 in.
Add up a tape in the app
The free Tape Calculator in the Fabora Steel Tools app adds and subtracts feet, inches and fractions the way you read a tape (shown with US settings). The free Unit Converter does the rest. The app works with no signal on iPhone and Android, and in your browser.
Fraction, decimal and mm questions
The ones that come up at the bench and on the phone to the supplier, answered with the numbers.
What is 5/8 as a decimal?
5/8 is 0.625 in, which is 15.875 mm. Divide 5 by 8 to get the decimal, then multiply by 25.4 for millimeters.
How do you convert a fraction to a decimal?
Divide the top number by the bottom number. 3/16 is 3 divided by 16, which is 0.1875. On the chart, find the fraction in the left column and read the decimal across.
How do you convert a decimal to a fraction?
Multiply the decimal by 64, round to the nearest whole number, then reduce the fraction. 0.7 x 64 = 44.8, so 45/64, which is 0.703125 in. Use 32 or 16 in place of 64 for a coarser fraction: 0.7 x 16 = 11.2, so 11/16.
How do you convert a fraction of an inch to mm?
Turn the fraction into a decimal, then multiply by 25.4. 3/16 is 0.1875 in, and 0.1875 x 25.4 = 4.7625 mm.
What is 1 mm in fractions of an inch?
1 mm is 0.0394 in. The nearest 1/64 is 3/64 in (0.046875 in), which is 0.0075 in over. The nearest 1/32 is 1/32 in (0.03125 in), which is 0.0081 in under.
What are the decimals for 1/16, 1/8, 1/4 and 1/2 inch?
0.0625, 0.125, 0.25 and 0.5 in, which are 1.5875, 3.175, 6.35 and 12.7 mm.
Which is bigger, 5/8 or 11/16?
11/16. Put both over 64: 5/8 is 40/64 and 11/16 is 44/64, so 11/16 is 4/64 (1/16) bigger. As decimals it is 0.6875 against 0.625.
Why does 1/32 show as 0.0313 on some charts and 0.03125 on others?
1/32 is exactly 0.03125. A chart that rounds to four places shows 0.0313. Both are right. This chart shows the 64ths in full, to six places, and rounds the other rows to four.
How far off can the nearest fraction be?
Never by more than half a step. The nearest 1/64 is within 0.0078 in (0.198 mm), the nearest 1/32 within 0.0156 in (0.397 mm) and the nearest 1/16 within 0.0313 in (0.794 mm). The converter shows the exact difference for your number.
Where these numbers come from
Nothing on this page is copied from another chart. The 64 rows are generated from the 64ths of an inch: the decimal is the fraction worked out, and the millimeter figure is that times exactly 25.4, the size of the inch agreed in 1959. The digits are written with whole-number arithmetic, so a tie such as 1/16 in = 1.5875 mm rounds up to 1.588 every time. Every row was checked against a second, independent calculation, and the well known ones hold: 1/4 in is 6.35 mm, 1/2 in is 12.7 mm and 1 in is 25.4 mm.
The converter works the same way. It picks the nearest 1/16, 1/32 and 1/64, with an exact tie rounding up, and shows whether that fraction is over or under your number. Always confirm a critical dimension against the drawing or the part.
Fabora Steel Tools
Tape measure math, in your pocket
The free Tape Calculator in Fabora Steel Tools adds and subtracts feet, inches and fractions the way you read a tape (shown with US settings), and the free Unit Converter does the unit conversions. It works with no signal on iPhone, Android and in your browser.
Works offlineFeet, inches and fractionsiPhone, Android and web