How are fractions written?

Fractions appearing by themselves in text should be written out:

three-fifths of a mile

one-half inch

increased by one-fourth

However, as a fractional expression becomes longer, readability dictates that the fraction be expressed as a numeral or a decimal:

18 1/4 revolutions

67/100 (or .67)

6 13/16 in.

Numerals should also be used when expressing measurements, especially in technical documents:

5/8-inch pipe

3 1/2 centimeters

2 3/4 gallons