Decimal inches to fraction.

Answer

3.854 in is closest to 3 7/8 in on a 1/8 in or 1/16 in ruler (3.875 in, 0.021 in off). To cut safely oversize and trim, the next size up at 1/16 in is 3 7/8 in.

Worked example

3.854 x 8 = 30.832, which rounds to 31, and 31/8 = 3 7/8. At 1/16 in: 3.854 x 16 = 61.664, rounds to 62, and 62/16 reduces to 3 7/8 as well. At 1/4 in: 3.854 x 4 = 15.416, rounds to 15, so 3 3/4. The same length is 97.9 mm (3.854 x 25.4) or 9.79 cm.

How it works

Multiply the decimal by the denominator, round to a whole number of steps (or round up for the next size up), and divide back, reducing the fraction. The error is the difference between the fraction and your decimal. One inch is exactly 25.4 mm, so millimetres are inches x 25.4. In quilting, the exact cut size for a unit such as a half-square triangle can be a decimal that no ruler shows, so you round to a ruler fraction.

Sources (opened 2026-10-08): Inch (Wikipedia).

FAQ

What is 0.875 as a fraction of an inch?

0.875 in is exactly 7/8 in.

How do I convert a decimal to the nearest 1/16 inch?

Multiply the decimal by 16, round to the nearest whole number and put that over 16, then reduce. For 3.854 that is 62/16, which reduces to 3 7/8.

Should I round up or to the nearest fraction?

Round to the nearest when you need accuracy. Round up when you plan to cut slightly oversize and trim, which is common for pieced units such as half-square triangles.

How many millimetres is an inch?

Exactly 25.4 mm. Multiply inches by 25.4 for millimetres.

Can I enter a fraction instead of a decimal?

Yes. Type 3 7/8, 3-7/8 or 7/8 and the tool converts it to a decimal and shows the nearest ruler fractions.