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Decimals, percentages and fractions

Choose between decimals, percentages, and fractions.

Decimals, percentages, and fractions each express a number as parts (or multiples) of a whole. They're usually interchangeable, but which form to use depends on the context.

Decimals

Use decimal numbers when you need to be precise, such as for measurements and values that the user needs to input. Don't use more precision than the content calls for. Three significant figures is usually enough.

Use a period as the decimal point separator. For numbers less than one, add a zero before the decimal point.

Don't use commas to separate digits to the right of the decimal point.

Avoid starting sentences with decimal values. Instead, rewrite the sentence.

IncorrectCorrect
0,5 kilograms0.5 kilograms
0.3456 meters per second0.345 meters per second

Percentages

Use percentages when you want to express a proportion or a change.

Write percentages with numerals. Don’t use a space between the numerals and the percent sign (%).

If you need to start a sentence with a percentage, then spell out both the number and the word "percent".

IncorrectCorrect
20 %20%
three hundred percent300%
30% of users in a recent study...Thirty percent of users in a recent study...

Preferably, rewrite the sentence to avoid starting with the percentage:
In a recent study, 30% of users....

Fractions

In general, don't write fractions as numbers in the form “a/b”. Convert the fraction to a decimal or percentage value, depending on the context.

You can write fractions as words like “half” or “two-thirds” in text when you don’t need to be precise.

Hyphenate spelled-out fractions. Connect the numerator and the denominator with a hyphen unless one of them is already hyphenated. In general, fractions with hyphenated numerators or denominators are clearer when you express them as decimals.

IncorrectCorrect
1/2 of participants50% of participants
1/4 of a yearA quarter of a year
1/3 of a pageone-third of a page
3/25three twenty-fifths

Preferably, express as a decimal or percentage:
  • 0.12
  • 12%