Inch fractions to decimals and millimetres
Every 32nd of an inch, reduced to its simplest form — the fractions you'll find on a tape measure, drill bits and spanners. One inch is exactly 25.4 mm.
| Fraction | Decimal | Millimetres |
|---|---|---|
| 1/32 | 0.03125 | 0.794 mm |
| 1/16 | 0.0625 | 1.588 mm |
| 3/32 | 0.09375 | 2.381 mm |
| 1/8 | 0.125 | 3.175 mm |
| 5/32 | 0.15625 | 3.969 mm |
| 3/16 | 0.1875 | 4.762 mm |
| 7/32 | 0.21875 | 5.556 mm |
| 1/4 | 0.25 | 6.35 mm |
| 9/32 | 0.28125 | 7.144 mm |
| 5/16 | 0.3125 | 7.938 mm |
| 11/32 | 0.34375 | 8.731 mm |
| 3/8 | 0.375 | 9.525 mm |
| 13/32 | 0.40625 | 10.319 mm |
| 7/16 | 0.4375 | 11.112 mm |
| 15/32 | 0.46875 | 11.906 mm |
| 1/2 | 0.5 | 12.7 mm |
| Fraction | Decimal | Millimetres |
|---|---|---|
| 17/32 | 0.53125 | 13.494 mm |
| 9/16 | 0.5625 | 14.288 mm |
| 19/32 | 0.59375 | 15.081 mm |
| 5/8 | 0.625 | 15.875 mm |
| 21/32 | 0.65625 | 16.669 mm |
| 11/16 | 0.6875 | 17.463 mm |
| 23/32 | 0.71875 | 18.256 mm |
| 3/4 | 0.75 | 19.05 mm |
| 25/32 | 0.78125 | 19.844 mm |
| 13/16 | 0.8125 | 20.638 mm |
| 27/32 | 0.84375 | 21.431 mm |
| 7/8 | 0.875 | 22.225 mm |
| 29/32 | 0.90625 | 23.019 mm |
| 15/16 | 0.9375 | 23.813 mm |
| 31/32 | 0.96875 | 24.606 mm |
| 1 | 1 | 25.4 mm |
How to add, subtract, multiply and divide fractions
Fractions follow a few simple rules. This calculator applies them and then reduces the answer to its simplest form, so you also see it as a decimal and a mixed number.
The rules
- Adding & subtracting: give both fractions the same denominator, then add or subtract the numerators. A quick way: a/b ± c/d = (a·d ± c·b) / (b·d).
- Multiplying: multiply the tops together and the bottoms together — a/b × c/d = (a·c)/(b·d).
- Dividing: flip the second fraction and multiply — a/b ÷ c/d = (a·d)/(b·c).
- Simplifying: divide the top and bottom by their greatest common divisor (GCD).
Worked example
1/2 + 1/3. Give them a common denominator of 6: 1/2 = 3/6 and 1/3 = 2/6. Add the numerators: 3/6 + 2/6 = 5/6. It's already in lowest terms, and as a decimal that's about 0.833.
Mixed numbers
When the top is bigger than the bottom (an "improper" fraction like 7/4), you can write it as a mixed number: 7 ÷ 4 = 1 remainder 3, so 7/4 = 1 3/4. The calculator shows both forms.
What is 3/8 as a decimal?
0.375 — 3 divided by 8. As a length, 3/8 inch is 9.525 mm.
What is 5/16 of an inch in mm?
7.938 mm (0.3125 × 25.4). A 5/16 drill bit is the nearest imperial size to an 8 mm bit.
What is 0.625 as a fraction?
5/8. 0.625 is 625/1000, and dividing top and bottom by 125 gives 5/8.
How do I add fractions with different denominators?
Convert both to the same denominator first. The shortcut is a/b + c/d = (a·d + c·b) / (b·d), then simplify. For 1/2 + 1/3 that's (3 + 2)/6 = 5/6. Enter the fractions above and the steps appear.
How do I multiply fractions?
Multiply the numerators together and the denominators together, then simplify. So 2/3 × 3/4 = 6/12 = 1/2. No common denominator is needed for multiplication.
How do I divide fractions?
Keep the first fraction, flip the second (its reciprocal), and multiply. So 1/2 ÷ 1/4 = 1/2 × 4/1 = 4/2 = 2. This is the "keep, change, flip" rule.
How do I turn a fraction into a decimal?
Divide the numerator by the denominator. For example 3/4 = 3 ÷ 4 = 0.75. Multiply by 100 to get the percentage (75%). See the reference table above for common ones.
What is a mixed number?
A mixed number combines a whole number and a fraction, like 1 3/4. You get it by dividing the numerator by the denominator: the whole part is the quotient and the remainder stays over the denominator. Need percentages instead? Try the percentage calculator.