1/8 as a decimal
1/8 = 0.125 inches = 3.175 mm.
0.125
1/8 of an inch
Millimetres
3.175 mm
Centimetres
0.3175 cm
Percent
12.5%
Decimal
terminates
8 goes into 1 0 times with 1 left over, so write 0 and a decimal point. Then bring down a zero and divide again, one digit at a time.
| Step | Divide | Digit | Subtract | Remainder |
|---|---|---|---|---|
| 1 | 10 ÷ 8 | 1 | 10 − 8 | 2 |
| 2 | 20 ÷ 8 | 2 | 20 − 16 | 4 |
| 3 | 40 ÷ 8 | 5 | 40 − 40 | 0 |
Remainder 0: nothing is left to divide, so the division stops and 1/8 = 0.125 exactly.
Where 1/8 falls at each precision, and whether the mark is the value exactly
| Rule | Nearest mark | Exact? |
|---|---|---|
| 1/16 | 1/8 | exact |
| 1/32 | 1/8 | exact |
| 1/64 | 1/8 | exact |
1/8 = 2/16 = 4/32 = 8/64
All the same mark. 1/8 is the form in lowest terms, which is how a rule labels it and how a cut list should read.
Mixed numbers with 1/8
A whole number of inches plus 1/8: the whole number goes in front of the decimal point and 1/8 supplies the digits after it
| Mixed | Inches | mm |
|---|---|---|
| 1 1/8 | 1.125 | 28.575 |
| 2 1/8 | 2.125 | 53.975 |
| 3 1/8 | 3.125 | 79.375 |
| 4 1/8 | 4.125 | 104.775 |
| 5 1/8 | 5.125 | 130.175 |
| 6 1/8 | 6.125 | 155.575 |
| 7 1/8 | 7.125 | 180.975 |
| 8 1/8 | 8.125 | 206.375 |
| 9 1/8 | 9.125 | 231.775 |
| 10 1/8 | 10.125 | 257.175 |
| 11 1/8 | 11.125 | 282.575 |
| 12 1/8 | 12.125 | 307.975 |
Converting 1/8 to a decimal
A fraction is a division. 1/8 = 1 ÷ 8 = 0.125. The decimal terminates because 8 factors into 2 × 2 × 2 — only 2s and 5s, the factors of ten. Any fraction whose denominator is built from those has an exact decimal.
In metric that is 3.175 millimetres (0.3175 cm), since one inch is exactly 25.4 mm. As a percentage of an inch it is 12.5%.
1/8 is a real mark on a rule: it is the 1/8 mark on a 1/16 rule, and the same mark is written 2/16 or 4/32 or 8/64 at finer precisions.
Going the other way
To turn 0.125 back into a fraction, pick the precision you are working to and multiply. At 1/16: 0.125 × 16 = 2, giving 1/8 exactly. At 1/32: 0.125 × 32 = 4, giving 1/8 exactly. At 1/64: 0.125 × 64 = 8, giving 1/8 exactly.
What is 1/8 as a decimal?
1/8 as a decimal is 0.125. Divide the numerator by the denominator: 1 ÷ 8 = 0.125. The division comes out exactly, with no remainder left over.
What is 2 1/8 as a decimal?
2 1/8 as a decimal is 2.125. The whole number stays in front of the decimal point and 1/8 supplies the digits after it, so 2 1/8 = 2 + 0.125. In millimetres that is 53.975 mm. This page's mixed-numbers table runs from 1 1/8 to 12 1/8.
What is 1/8 as a percent?
1/8 as a percent is 12.5%. Multiply the decimal by 100: 0.125 × 100 = 12.5%.
What is 0.125 as a fraction?
0.125 as a fraction is 1/8, in lowest terms. It can also be written 2/16 or 4/32 or 8/64, which are the same value expressed over a larger denominator.
How many millimetres is 1/8 of an inch?
1/8 of an inch is 3.175 mm, or 0.3175 cm. An inch has been defined as exactly 25.4 mm since 1959, so this conversion is a definition rather than a measurement — the millimetre value is exact too.
Where is 1/8 on a tape measure?
1/8 is a real mark on a rule: it is the 1/8 mark on a 1/16 rule, and the same mark is written 2/16 or 4/32 or 8/64 at finer precisions.