Key Takeaways
- In academic English, a sentence should not begin with a numeral. “200 participants” at the start of a sentence is incorrect. Write “Two hundred participants” or rephrase the sentence.
- The two solutions are: spell out the number (“Thirty samples were collected”) or restructure the sentence so the number is not first (“A total of 30 samples were collected”).
- Numbers from one to nine (or one to ten, depending on the style guide) are spelled out in running text. Numbers 10 and above are written as numerals.
- This rule applies to all academic style guides (APA, Chicago, AMA, IEEE). Reviewers and editors flag it consistently.
- PM Proofreading’s editing service checks for correct number formatting across your manuscript.
This is one of the simplest rules in academic writing, and one of the most frequently broken: do not start a sentence with a numeral. “50 participants were recruited” is incorrect. “Fifty participants were recruited” is correct. So is “A total of 50 participants were recruited.”
The rule exists because a numeral at the start of a sentence can be misread. After a period, the reader expects a capital letter. A numeral disrupts that expectation and can cause momentary confusion, especially in dense text with many numbers.
This guide covers the rule, the exceptions, and the broader conventions for writing numbers in academic text.
The Rule and How to Apply It
When a number falls at the beginning of a sentence, you have two options.
Option 1: Spell it out. “Thirty samples were analysed.” “Two hundred and forty respondents completed the survey.” This works well for round numbers and smaller numbers. It becomes awkward for precise or large numbers: “One thousand two hundred and thirty-seven data points were collected” is technically correct but unreadable.
Option 2: Restructure the sentence. “A total of 1,237 data points were collected.” “The survey received 240 responses.” “Of the samples tested, 30 showed contamination.” This is usually the better option for large or precise numbers.
The restructuring approach is more flexible and avoids the awkwardness of spelling out large numbers. Most experienced academic writers default to restructuring rather than spelling out.
General Rules for Numbers in Academic Writing
Different style guides have slightly different rules, but the core conventions are consistent across most.
APA (7th edition): Spell out numbers zero through nine. Use numerals for 10 and above. Exceptions: always use numerals for measurements, ages, scores, times, dates, and numbers in tables and figures. Always spell out any number that begins a sentence.
Chicago Manual of Style: Spell out numbers zero through one hundred (more conservative than APA). Use numerals for 101 and above. This convention is more common in humanities writing.
AMA and scientific style: Use numerals for all numbers 10 and above and for any number followed by a unit of measurement (5 mL, 3 kg, 2 h). Spell out numbers below 10 unless they are part of a measurement.
Regardless of style guide, certain contexts always use numerals: page numbers, figure and table numbers, statistical values (p < 0.05, r = 0.82), percentages (12%), and mathematical expressions.
Consistency Within a Sentence
When a sentence contains two or more numbers referring to the same category, use the same format for all. “The study included 3 schools and 120 students” is inconsistent (3 is below 10 and would normally be spelled out, but 120 cannot be). The correct approach is: “The study included 3 schools and 120 students” (use numerals for both, since they are in the same category and at least one requires a numeral). APA specifically states that when numbers above and below 10 appear in the same sentence referring to the same category, use numerals for all of them.
However, numbers referring to different categories within the same sentence can follow their own rules. “Three experiments were conducted with 200 participants each” is correct because “three” (experiments) and “200” (participants) are different categories.
Other Number Formatting Conventions
Thousands separators. Use a comma for numbers of four or more digits in American English: 1,000; 10,000; 1,234,567. Some European and international conventions use a period or space instead. Check your journal’s style.
Decimal points. Use a period in American and British English: 0.05, 3.14. Some European conventions use a comma. In academic writing in English, always use a period.
Ranges. Use an en dash for number ranges: pages 45-67, years 2015-2023. Write “from 2015 to 2023” (not “from 2015-2023”). For more on dash usage, see our post on hyphens, en dashes, and em dashes.
Units. Always include a space between the number and the unit: 5 kg, 100 mL, 37 °C. See our post on spacing between numbers and unit symbols for the full conventions.
Conclusion
The “no numeral at the start of a sentence” rule is easy to remember and easy to apply. Restructure the sentence or spell out the number. For general number formatting, check your style guide and apply it consistently. These are small details, but they contribute to the overall polish of your manuscript and signal to reviewers that you have taken care with the writing.
Need your manuscript checked for formatting consistency? PM Proofreading’s editing service checks number formatting, units, punctuation, and style guide adherence. Upload your manuscript and get a quote.
Further Reading
- Overall English Grammar Review for Non-Native Researchers
- Space Between Number and Temperature Degree Symbol
- Hyphen, En Dash, and Em Dash: What Is the Difference?
- A Quick Guide to Punctuation for Non-Native Researchers
Frequently Asked Questions
Can I ever start a sentence with a numeral?
No. All major academic style guides (APA, Chicago, AMA, IEEE) prohibit starting a sentence with a numeral. Either spell out the number or restructure the sentence so the number does not come first. There are no exceptions to this rule in standard academic writing.
When should I spell out numbers vs use numerals?
APA: spell out zero through nine, use numerals for 10+. Chicago: spell out zero through one hundred, numerals for 101+. AMA/scientific: numerals for all numbers with units. Always use numerals for measurements, statistics, percentages, and figures. Check your specific style guide and apply it consistently.
How do I handle two different numbers next to each other?
Spell out one and use numerals for the other to prevent confusion. “Twelve 5-mL samples” is clearer than “12 5-mL samples.” Generally, spell out the first number and use numerals for the second, or whichever order is clearest.
Should I write “percent” or use the % symbol?
APA and most scientific styles use the % symbol with a numeral: “12%” (with no space between number and symbol). Chicago recommends spelling out “percent” in running text. In tables and figures, use the % symbol regardless of style guide. Check your journal’s convention.
