There is a rule about when to write numbers as words, and when not to. My source is the Style Manual for authors, editors and printers. Sixth edition, published by John Wiley & Sons in 2002.
If you read that previous sentence again you will see an example of what I am talking about. Sixth is written as a word, not as 6th. And why? Because it’s less than ten. And yes, there’s a section on whether you can start a sentence with the word because as well. That’s for another post.
In essence, numbers from zero to ten are written as words, and numbers higher than that use numerals, such as my age which is a powerfully big number - 62.
Of course ,you will see exceptions to that, even on this site. I have chosen to call my writing model 10 terrific tactics because it looks good on the page, and I think it’s easier for people to remember. That wasn’t an automatic decision though, my dear reader, I did spend time ruminating on it. Probably for far too long. (Procrastination hem!)
There are 13 pages in the Style Guide explaining currency, using words not numerals to start a sentence and all the other complexities. All I wanted to do here was to remind you of the essential rule.
And there you have it. Simple to remember and easy to do. Follow it and you will look professional.
Zero to ten, 11 up.