[header] How to spell numbers [title] Spell out the numbers one through nine. [step] Unless you are short on space, this is the most widely accepted way to write a single-digit number. [title] Spell out " zero " as well. 
[step] You may also spell it as " zed " if using the uk english accepted spelling. Since it can be easily mistaken for the letter " o " it is best to treat it as if it were a single-digit number.