Spell out numbers less than 10 (including zero) or any number that begins a sentence. However, for email subjects and timestamps, you may use numerals.
Do
- "Eight new employees started on Monday, and 12 start next week."
- "Daniel won first place in last year's hackathon, which had 75 participants."
Don't
- "8 new employees started on Monday, and twelve start next week."
- "Daniel won first place in last year's hackathon, which had seventy-five participants."
Exceptions to the above rule: numerals should always be used for addresses, temperatures, times, speed, and percentages.
Do
- "Productboard is located at Boudnikova 3, Prague 8."
- "This feature's status was last updated at 12:03 p.m."
- "Total progress is currently at 75%."
When referring to ‘millions’ and ‘billions’, its often best to use a mix of numbers and words for visual clarity and space. For numeric figures, you can opt to use up to two decimal points to round off your number.
Do
- "The project will cost around $2.34 million."
- "This company has over 1 billion customers."
Don't
- "The project will cost around $2,340,000."
- "This company has over 1,000,000,000 customers."
If the number is part of an expression that typically uses spelled-out numbers, leave them that way.
Do
- "A great onboarding experience makes a great first impression."
- "We need to add a third-party integration."
- "Build the best products using the all-in-one product management system."
Don't
- 1st impression
- 3rd-party integration
- all-in-1
Use commas for numbers with more than three digits (but words for millions, billions, and trillions):
Do
- 1,000
- 150,643
- 4 million
- 65 billion
Don't
- One thousand
- 150.643 thousand
- 4,000,000
- 65,000,000,000