What are Numbers?
English has two ways to express numerical values: words (three, forty-five, two hundred) and digits (3, 45, 200). Which form to use depends on the number itself, its context (running prose vs data), what comes before it, and the style guide in use. There is no single universal rule, but there are widely accepted conventions that apply across academic and professional writing.
The most common rule is the threshold rule: spell out numbers from one to nine (or one to ten in some style guides) and use digits for 10 (or 11) and above. However, this rule has many exceptions: digits are preferred with units of measurement, times, dates, percentages, and statistics regardless of size. Words are required at the start of a sentence regardless of size.
Consistency within a document matters as much as the individual choice. If you are comparing multiple numbers in one sentence or paragraph, use the same form for all of them: 'The three groups had 4, 9, and 14 participants' follows the principle of consistency even though 4 and 9 would normally be spelled out.
Core Number Rules
Apply the rules in this order: start-of-sentence rule first, then context rule (units/statistics), then the threshold rule for everything else.
Spell out 1–9 in prose / use digits for 10+ / always spell out at start of sentence / always use digits with units and statisticsThreshold Rule (General Prose)
| Situation | Use words | Use digits |
|---|---|---|
| Numbers 1–9 in running prose | three candidates, nine countries | — |
| Numbers 10 and above in running prose | — | 14 respondents, 200 entries |
| Round numbers and approximate figures | about twenty people, a hundred reasons | also acceptable: about 20 people |
| Large round numbers (millions, billions) | three million, half a billion | 3 million, 0.5 billion |
Context Rules (Override Threshold)
| Context | Always use digits | Example |
|---|---|---|
| Times | always digits with times | The meeting starts at 9:30 a.m. / 14:00 |
| Dates | day and year in digits | 12 March 2024 / March 12, 2024 |
| Percentages | always digits + % | The approval rate was 7%, not 'seven percent' in data |
| Units of measurement | always digits + unit | 3 km, 8 kg, 500 ml, 2 hours |
| Statistics and data | always digits in tables and data | a ratio of 3:1 / 4 out of 5 participants |
| Money | always digits + currency symbol | $14.50 / £8 / €250 |
| Scores and results | always digits | The vote was 6–4 in favour. |
Special Cases
| Situation | Rule | Example |
|---|---|---|
| Start of a sentence | always spell out — no digits to open a sentence | Fourteen candidates applied. (NOT: 14 candidates applied.) |
| Two numbers adjacent | spell out one to avoid confusion | She submitted three 10-page reports. |
| Fractions in prose | spell out simple fractions | two-thirds of the respondents, one-quarter of the budget |
| Ordinals in prose | spell out first–ninth; digits for 10th+ | the third attempt, the 12th edition |
| Consistency in a list | if one number exceeds threshold, use digits for all | groups of 4, 9, and 14 (not: four, nine, and 14) |
Key Number Writing Contexts
Numbers at the start of a sentence
Never begin a sentence with a digit. Spell out the number in full, or rewrite the sentence so the number does not appear first. This rule overrides every other number rule.
- Incorrect: 47 delegates attended the summit.
- Correct: Forty-seven delegates attended the summit.
- Or rewrite: A total of 47 delegates attended the summit.
- Incorrect: <hl>2024</tml> was a significant year for the programme.
- Correct: The year 2024 was significant for the programme.
Numbers with units of measurement
When a number accompanies a unit of measurement, always use a digit — even if the number is below 10. Place a space between the digit and the unit symbol (except for percentages and currency symbols in some style guides).
- Measurement: The container holds 5 litres.
- Distance: She ran 8 km before sunrise.
- Time duration: The session lasted 3 hours.
- Percentage: The error rate dropped to 4%.
- Currency: The cost rose to £9 per unit.
Consistency in comparisons and lists
When comparing multiple numbers in one clause or sentence, use the same form for all of them. If any number in the group exceeds the threshold (9 or 10), use digits for the entire group.
- Inconsistent: The three groups contained four, nine, and 14 participants.
- Consistent: The three groups contained 4, 9, and 14 participants.
- Inconsistent: Between 5 and fifteen respondents were selected.
- Consistent: Between 5 and 15 respondents were selected.
Number Warning Signals
Words vs Digits — Same Context, Different Rules
The same number uses different forms depending on context. Units, statistics, and starts of sentences override the basic threshold rule.
General prose — spell out 1–9
Three countries submitted objections to the proposal.
Three is below the threshold (10) and has no unit — spell out.
With a unit of measurement — always digits
The package weighs 3 kg and must be shipped within 5 days.
3 kg uses digits because of the unit. 5 days uses digits for consistency in the same clause.
Common Mistakes
Starting a sentence with a digit
✗ 47 participants completed the survey.
Forty-seven participants completed the survey. / A total of 47 participants completed the survey.
Sentences never begin with a digit in standard edited English. Spell out the number or restructure the sentence.
Spelling out numbers with units of measurement
✗ The package weighs eight kilograms and is three metres long.
The package weighs 8 kg and is 3 m long.
Numbers with units always use digits, regardless of whether the number is below 10. Spelling out both the number and the unit ('eight kilograms') is acceptable in very informal prose but uncommon in professional or academic writing.
Inconsistent number forms in a comparison
✗ The first group had five members, the second had 11, and the third had 8.
The first group had 5 members, the second had 11, and the third had 8.
When numbers appear in a comparable series, use one consistent form. Since 11 exceeds the threshold, switch all numbers in the series to digits.
Mixing spelled-out fractions and digits
✗ About one-third of respondents (33.3%) disagreed.
About one-third of respondents disagreed. / About 33% of respondents disagreed.
This is not always wrong, but mixing a spelled-out fraction with a percentage in parentheses is redundant. Choose one form and stay with it.
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