There are different conventions for writing numbers. A common convention is to use words for numbers up to nine, and numerals thereafter:

  There were 10 requests: four from the bowling club, three from the surf club, and three from anonymous individuals.

Always use words for numbers at the beginning of a sentence:

  Fifty-six submissions were examined; 24 were rejected.

Use numerals for numbers accompanied by a symbol:

  86 km   32°C   2%   $54.31

If a symbol is written in full, the accompanying numeral can be written as a number:

  44 degrees   96 per cent

In narrative or descriptive text, words may be more appropriate for both numbers and measurements:

  My goal is to run fifteen kilometres.

  ‘Hey, you owe me thirty-two dollars!’