Use words for some numbers
Sometimes, it’s best to write out the word instead of using numerals. A common convention is to write out all numbers less than 10 (or less than 100 in some styles) that aren’t dates, labels or measurements.
Good use – prose: There were three approaches, each with two components.
Good use – measurement: The calculated time was 4.3 seconds.
Good use – date: We looked at news headlines from 6 August 2006.
It’s also common to write out words instead of using numerals is when the number is approximated or rounded.
Common use: There were approximately three hundred artifacts.
Common use: Almost one million people were at the rally.
Unless they are part of a calculation, fractions are generally written out in full. For example, you might see “three-fifths of the pizza remained” or “one third of the population was affected.”