numbers: fractions

In non-technical writing, spell out simple fractions, especially when they are used in isolation:

• half of one percent
• half an inch or one-half inch
• a quarter of an inch or one-quarter inch
• three quarters of an inch or three-quarters inch (not inches)
• three-quarter length

When a fraction is used adjectivally, place a hyphen between the numerator and the denominator unless either of these elements is itself hyphenated:

• four-fifths inch
• a three-quarters majority

Fractions such as the last two, which lend themselves to confusion, are better expressed in numerals.

For the use of hyphens with fractions, see hyphens: fractions.

It is incorrect to use “th” or “ths” after fractions expressed in numerals:

• 1/25 (not 1/25th)
• 3/100 (not 3/100ths)

A fraction expressed in numerals should not be followed by “of a” or “of an”:

• 3/8 inch (not 3/8 of an inch)

If the sentence seems to require “of a,” the fraction should be spelled out.

Mixed numbers (combinations of a whole number and a fraction) should be given in numerals:

• 2¾ but time and a half for overtime