What is the general rule for expressing numbers in numeric form versus spelling them out?

The rationale behind the guideline that numbers under 10 should be spelled out, while numbers 10 and above may be expressed in numeric form, is rooted in clarity and readability in writing. This convention helps maintain a smooth flow in texts, especially in professional and academic contexts.

When numbers are kept to single digits, spelling them out (like one, two, three) often makes the text easier to read and more aesthetically pleasing, allowing for a more engaging reading experience. On the other hand, numbers that are 10 and above tend to be more cumbersome when spelled out and are typically expressed in numeric form (such as 10, 15, 20). This approach allows for quicker comprehension, particularly in data-heavy documents or in instances where precision is crucial.

By following this guideline, writers can enhance the clarity of their communications, making the text more user-friendly for readers.