Decimal to Fraction Calculator

The calculator updates as you type, so there is no button to press. Decide first whether you want the exact fraction or a practical one that matches the marks on a tool.

1. Type your number in the Decimal box, for example 0.375 or 2.75. Negative numbers work, and commas are ignored. Percent signs, fractions and scientific notation are not accepted.
2. Open Fraction type. Choose Exact (as typed) for homework and recipes. Choose Nearest 1/16 (rulers), 1/8, 1/32 or 1/64 when you need a mark on a tape measure or a drill bit size, and Nearest 1/100 for hundredths.
3. Choose Nearest, denominator up to 1000 when the decimal is a rounded version of something like one third and you want the simple fraction behind it.
4. Read the large fraction at the top, then the Mixed number, Fraction as a decimal, Percentage and Difference from your decimal rows.
5. Check the table of the nearest 1/2, 1/4, 1/8, 1/16, 1/32, 1/64 and 1/100, each with its error, to see how much accuracy a coarser ruler costs you.

Typical jobs are reading a decimal inch from a spec sheet or caliper as a tape-measure fraction, picking a drill bit or wrench size, scaling a recipe whose quantity came out as a decimal, and checking school fraction homework. If the answer will be cut, drilled or poured, look at the error row before you trust a rounded fraction.

Every decimal that ends is a fraction with a power of ten underneath it. Write the digits over 10, 100, 1000 and so on, using as many zeros as there are decimal places, then divide the top and bottom by their greatest common divisor. In exact mode the tool does this for up to 9 decimal places.

Take 0.375. Three places means a denominator of 1000, so the fraction starts as 375/1000. The greatest common divisor of 375 and 1000 is 125, and dividing both by it gives 3/8. Take 2.75: that is 275/100, which reduces by 25 to 11/4, or the mixed number 2 3/4. A negative input keeps its sign, so -0.125 becomes -1/8.

A decimal with more than 9 places, such as 3.14159265358979, cannot be written over a manageable power of ten. For those the tool finds the closest fraction with a denominator up to 100,000 and tells you it did so. A shorter value such as 3.14159 stays exact: it is 314159/100000, which does not reduce further. For related arithmetic with fractions, the fraction calculator adds, subtracts, multiplies and divides them.

A ruler only has marks at fixed spacings, so a decimal usually has to be rounded. The tool multiplies the decimal by the denominator, rounds to the nearest whole number and reduces the result. For 0.7 and a 1/16 ruler, 0.7 x 16 = 11.2, which rounds to 11, so the answer is 11/16. That equals 0.6875, and the Difference from your decimal row shows 0.0125. Exact mode would instead give 7/10 with no error. The table lists every denominator side by side: for 0.7 the nearest 1/8 is 3/4 (off by 0.05), the nearest 1/64 is 45/64 (off by 0.00313) and the nearest 1/100 is 7/10 (exact).

The tool does not recognize repeating decimals as such. If you type 0.3333 in exact mode you get 3333/10000, because that is what the digits say. Switch to Nearest, denominator up to 1000 and the answer becomes 1/3, with a difference of about 0.0000333 shown so you can judge it. The same trick turns 0.6667 into 2/3. It is a closest-fit search, so type enough digits for the fraction you expect. A short decimal such as 0.33 is already an exact fraction (33/100), so the search will return that rather than 1/3. Judge the answer by the difference row.

When you only care about the nearest convenient mark, 1/16 is the usual compromise for woodworking and home projects, 1/32 or 1/64 suits machining and fine work, and 1/8 is enough for rough cuts. A finer denominator always gives a smaller error, but a mark you cannot read on your tape is no use, so match the setting to the tool in your hand.

Common mistakes are reading the wrong ruler, since a 1/16 mark and a 1/8 mark look similar, and rounding twice, once in your head and once in the tool. Convert the original measurement, not an already rounded one. To change the unit as well, try the inches to millimeters converter or the feet to inches converter, and use the percentage calculator when the percentage row is what you need.