Words and digits
We use words for single-figure numbers, digits for anything above nine. i.e., eight, nine, 10, 11, 12 - except with abbreviated units of measurement, e.g., 3kg, and with percentages, e.g., 4%.
If there are more than three digits, we use a comma to separate, i.e., 1,000 or 128,039.
Don’t start a sentence or headline with digits, e.g., Seventeen percent increase year-on-year, except with listicles, where using a digit may better suit the tone of the article.
Millions and billions are spelled out, e.g., five million people, 10 billion transactions, except where they are used with currencies or in headlines, e.g., £5m, £20bn, GBG Instinct saves customer £500m in one year. And remember that billion is widely accepted as meaning one thousand million (not one million million).
But all numbers are expressed as digits if the accompanying units are abbreviated, e.g., 50p, £5, £60, £3m, £500m, £6bn, £20bn, £15tn.
Use an en-dash (–) to indicate number ranges or page ranges 17–22, 20,000–27,000, or pages 23–37.