Why use Decimal to Fraction Converter
This converter turns a decimal into an exact fraction and shows the working. A terminating decimal is written over a power of ten and reduced, so 0.625 becomes 625/1000 and then 5/8. A repeating decimal is entered with the repeating digits in brackets, so 0.1(6) becomes 1/6 and 0.(3) becomes 1/3. Values above 1 are also given as a mixed number: 2.75 is 11/4, or 2 3/4. The Nearest fraction option adds the closest practical fraction, such as the nearest 1/16 for reading a decimal inch measurement on a tape measure, and says how far off it is. The conversion uses whole-number arithmetic, so nothing is rounded unless you ask for it.
Decimal to fraction chart for common values
Every row is the converter's output. Brackets mark repeating digits. The last column is the nearest sixteenth, for inch measurements.
| Decimal | Fraction | Percent | Nearest 1/16 |
|---|---|---|---|
| 0.05 | 1/20 | 5% | 1/16 |
| 0.0625 | 1/16 | 6.25% | 1/16 (exact) |
| 0.08(3) | 1/12 | 8.(3)% | 1/16 |
| 0.1 | 1/10 | 10% | 1/8 |
| 0.(1) | 1/9 | 11.(1)% | 1/8 |
| 0.125 | 1/8 | 12.5% | 1/8 (exact) |
| 0.(142857) | 1/7 | 14.(285714)% | 1/8 |
| 0.15 | 3/20 | 15% | 1/8 |
| 0.1(6) | 1/6 | 16.(6)% | 3/16 |
| 0.2 | 1/5 | 20% | 3/16 |
| 0.25 | 1/4 | 25% | 1/4 (exact) |
| 0.3 | 3/10 | 30% | 5/16 |
| 0.3125 | 5/16 | 31.25% | 5/16 (exact) |
| 0.(3) | 1/3 | 33.(3)% | 5/16 |
| 0.375 | 3/8 | 37.5% | 3/8 (exact) |
| 0.4 | 2/5 | 40% | 3/8 |
| 0.45 | 9/20 | 45% | 7/16 |
| 0.5 | 1/2 | 50% | 1/2 (exact) |
| 0.6 | 3/5 | 60% | 5/8 |
| 0.625 | 5/8 | 62.5% | 5/8 (exact) |
| 0.(6) | 2/3 | 66.(6)% | 11/16 |
| 0.7 | 7/10 | 70% | 11/16 |
| 0.75 | 3/4 | 75% | 3/4 (exact) |
| 0.8 | 4/5 | 80% | 13/16 |
| 0.8(3) | 5/6 | 83.(3)% | 13/16 |
| 0.875 | 7/8 | 87.5% | 7/8 (exact) |
| 0.9 | 9/10 | 90% | 7/8 |
| 1.25 | 5/4 = 1 1/4 | 125% | 1 1/4 (exact) |
| 1.5 | 3/2 = 1 1/2 | 150% | 1 1/2 (exact) |
| 2.75 | 11/4 = 2 3/4 | 275% | 2 3/4 (exact) |
0.33 and 0.67 are not thirds: 0.33 is exactly 33/100 and 0.67 is exactly 67/100. Use 0.(3) and 0.(6) for 1/3 and 2/3.
Tenths of an inch as ruler fractions
Decimal inches from a calculator, drawing or digital caliper rarely land on a ruler mark. These are the closest marks at each precision.
| Decimal inches | Nearest 1/8 | Nearest 1/16 | Nearest 1/32 | Nearest 1/64 |
|---|---|---|---|---|
| 0.1 | 1/8 | 1/8 | 3/32 | 3/32 |
| 0.2 | 1/4 | 3/16 | 3/16 | 13/64 |
| 0.3 | 1/4 | 5/16 | 5/16 | 19/64 |
| 0.4 | 3/8 | 3/8 | 13/32 | 13/32 |
| 0.5 | 1/2 | 1/2 | 1/2 | 1/2 |
| 0.6 | 5/8 | 5/8 | 19/32 | 19/32 |
| 0.7 | 3/4 | 11/16 | 11/16 | 45/64 |
| 0.8 | 3/4 | 13/16 | 13/16 | 51/64 |
| 0.9 | 7/8 | 7/8 | 29/32 | 29/32 |
| 1.4 | 1 3/8 | 1 3/8 | 1 13/32 | 1 13/32 |
| 2.65 | 2 5/8 | 2 5/8 | 2 21/32 | 2 21/32 |
| 5.3 | 5 1/4 | 5 5/16 | 5 5/16 | 5 19/64 |
A value exactly halfway between two marks is rounded up. Fractions are simplified, so 6/32 is shown as 3/16.
The formula for terminating and repeating decimals
Terminating: digits / 10^n, where n is the number of decimal places. Repeating: (all digits through one repeat - digits before the repeat) / (10^n x (10^r - 1)), where n is the count of non-repeating places and r is the length of the repeat. Then divide both parts by their GCD.
For 0.1(6), n is 1 and r is 1: the digits through one repeat are 16 and the digits before the repeat are 1, so the fraction is (16 - 1)/(10 x 9) = 15/90 = 1/6. For 1.2(34), n is 1 and r is 2, giving (1234 - 12)/(10 x 99) = 1222/990 = 611/495. The rule comes from algebra: multiplying x by two different powers of ten lines up the repeating tails so that subtracting one from the other cancels them. A pure repeat such as 0.(142857) simply sits over as many nines as it has digits: 142857/999999, which reduces to 1/7.
Worked conversions
A terminating decimal
Decimal 0.625; Nearest fraction Nearest 1/16
5/8. Before simplifying 625/1000, divided top and bottom by 125. Nearest 1/16: 5/8, exact. Percent 62.5%.
A decimal greater than 1
Decimal 2.4375; Nearest fraction Nearest 1/4
39/16 = 2 7/16. Before simplifying 24,375/10,000, divided by 625. Nearest 1/4: 2 1/2, which is 0.0625 too big.
A repeating decimal with a non-repeating start
Decimal 1.2(34); Nearest fraction Closest with denominator up to 100
611/495 = 1 116/495. The closest fraction with a denominator up to 100 is 1 15/64, 0.000032 too big.
A negative decimal
Decimal -1.75; Nearest fraction Nearest 1/8
-7/4 = -1 3/4. Nearest 1/8: -1 3/4, exact.
A long decimal approximated by a small fraction
Decimal 3.14159; Nearest fraction Closest with denominator up to 1,000
Exact: 314,159/100,000, already in lowest terms. Closest with a denominator up to 1,000: 3 16/113 (that is 355/113), 0.000003 too big. With a limit of 10 it is 3 1/7.
A percent
Decimal 12.5%; Nearest fraction Nearest 1/16
1/8. A trailing percent sign divides by 100 first: 125/1000 reduces to 1/8.
Ruler fractions versus the closest fraction of any denominator
The two groups in the Nearest fraction menu answer different questions. A ruler option rounds to the closest multiple of one division, 1/2, 1/4, 1/8, 1/16, 1/32 or 1/64, and then simplifies it. This is the one to use for inches, drill bits and wrench sizes, where only those denominators exist. The Nearest ruler fractions table lists all six at once with the size and direction of the error, so you can decide whether a sixteenth is close enough or the job needs a sixty-fourth.
The Any denominator options find the single closest fraction whose denominator does not exceed 10, 100 or 1,000. This is how a measured or rounded value is traced back to a simple ratio: 0.714 gives 5/7 with a limit of 10, and 0.33 gives 1/3. It cannot know what you meant, so treat the result as a suggestion and check the difference shown beside it.
A few limits apply. Recurring digits must be marked with brackets; a row of dots such as 0.333... is rejected rather than guessed at. Numbers are limited to 30 digits. A decimal comma such as 0,75 is read as 0.75. To go the other way, from a fraction to a decimal, use the fraction calculator, which shows the decimal for any fraction you enter.
How to use it
- 1
Type the number in the Decimal box, for example 0.625, 1.75 or -0.4.
- 2
For a repeating decimal, put the repeating digits in brackets: 0.(3) for 0.333... or 0.1(6) for 0.1666...
- 3
Choose a Nearest fraction option: a ruler fraction from 1/2 to 1/64, or the closest fraction with a denominator up to 10, 100 or 1,000.
- 4
Read the Fraction and Mixed number, then the Working, step by step table to see the GCD used.
- 5
Check the Nearest ruler fractions table for the value rounded to each ruler division and the difference from the exact value.