Always keep the format clear, such as “(555) 123-4567” or “555-123-4567” when including credit card or contact details.
Example: “Never give out your credit card number over the phone.”
Numbers are an essential part of communication. Whether you’re writing a report, sending an invoice, or drafting an essay, numbers help convey clear and precise information. Here’s a guide to help you use numbers effectively in your writing.
When to Use Numbers as Words or Digits
number in a sentence
Write out numbers from one to nine in words (e.g., “Think of a number between one and nine”).
Use digits for numbers 10 and above (e.g., “There are 15 students in the class”).
For large numbers, combine words and digits (e.g., “5 million residents”).
Always keep the format clear, such as “(555) 123-4567” or “555-123-4567” when including credit card or contact details.
Example: “Never give out your credit card number over the phone.”
Lists or Sequences
Use numbers to order items or provide clear instructions, such as “Step 1, Step 2.”
Example: “Each page is neatly numbered in the top corner of the document.”
Statistics and Percentages
Use numbers to convey precise data and trends easily in sentences, especially for analytics reports.
Example: “The team achieved a 25% increase in sales revenue.”
Dates & Time
Simplify timelines with numerical date formats (e.g., “April 15, 2023” or “10 AM”).
Example Applications for Numbers
Expressing Quantities Clearly:
Use numbers to emphasize quantity or size with clarity. Example from a budget breakdown or example-style story structure.
The “spell it out or use digits” rule that finally stuck for me
During my IELTS writing practice I kept dropping easy marks because I couldn’t decide whether to write “five” or “5.” I basically flipped a coin every time. Then a classmate at Lund showed me the rule her Swedish school had drilled into her, and it’s the one I still lean on.
Spell out the small ones. One to ten, write as words. “I read three books last month.” It just reads cleaner inside a sentence.
Switch to digits for the bigger ones. From 11 up, use figures. “The class had 27 students.” Nobody wants to wade through “twenty-seven” mid-paragraph.
Never open a sentence with a digit. This is the rule people forget most. “15 students passed” looks wrong at the start of a line. Either spell it — “Fifteen students passed” — or rewrite so the number sits further in.
Where most learners slip
They mix the two styles in the same paragraph: “I bought 3 pens and seven notebooks.” Pick one logic and hold it across the whole piece. The exception I actually like: if two numbers sit next to each other, spell one to avoid a pile-up, so “twelve 50-page notebooks,” not “12 50-page notebooks.”
A few quick calls I make without thinking now. Money and percentages get digits — 20%, 50 kr — because that’s how we read them in real life. Big round numbers can stay words when you want a softer tone: “about a thousand people,” not “about 1,000 people.” And times are your choice, but be consistent: 7 a.m. all the way through, or seven in the morning all the way through. Don’t swap halfway.
Here’s a thirty-second test for your own writing: read the sentence out loud. If you’d say the number as one short word, it can usually be a word on the page too. If you’d rattle off the digits, write the digits. What’s the longest number you’ve ever spelled out in an essay because a teacher told you to? Mine was a painful one, and it taught me this rule the hard way.
Aarav Mehta is the founder of EnglishProGuide. He taught himself English to an IELTS 7.5 without any formal coaching, and now shares the practical grammar lessons, real examples, and study tips that actually worked for him.
