In professional writing, numbers and percentages must be formatted correctly for clarity, readability, and consistency. Choosing between numerals and spelled-out numbers, formatting large figures, and using percentages correctly can significantly impact the professionalism of your writing.
This guide provides essential rules and examples to help you format numbers and percentages correctly in professional documents.
1. When to Spell Out Numbers vs. Use Numerals
Whether to spell out numbers or use numerals depends on context, readability, and style guide recommendations.
General Rules:
✔ Spell out numbers one through nine (1–9) in formal writing.
✔ Use numerals for numbers 10 and above (10+).
Examples:
• Correct: The report includes three main findings.
• Correct: The survey was conducted with 15 participants.
✔ Spell out numbers that begin a sentence, regardless of size.
Examples:
• Incorrect: 25 employees attended the conference.
• Correct: Twenty-five employees attended the conference.
✔ For numbers in a series, keep formatting consistent.
Examples:
• Correct: The company hired three managers, 12 analysts, and 25 interns.
• Incorrect: The company hired three managers, twelve analysts, and 25 interns.
Best Practices:
• If clarity is an issue, use numerals even for numbers below 10.
• If a style guide (e.g., APA, MLA, Chicago) applies, follow its specific rules.
2. Formatting Large Numbers
Large numbers require proper formatting to improve readability and avoid misinterpretation.
Use Commas for Thousands and Higher:
✔ Always use commas to separate thousands, millions, and billions in professional writing.
Examples:
• Correct: The company generated $1,250,000 in revenue last year.
• Correct: The study analyzed data from 10,500 participants.
• Incorrect: The company generated $1250000 in revenue last year.
Use Words for Rounded Large Numbers:
✔ When expressing rounded large numbers, use a combination of numerals and words.
Examples:
• Correct: The project costs approximately 3 million dollars.
• Correct: Over half a billion people use this software.
✔ Use numerals for exact figures but words for estimates or generalizations.
Examples:
• Exact: The city’s population is 2,385,000.
• Estimate: The city has nearly 2.4 million residents.
3. Formatting Percentages in Professional Writing
Percentages must be formatted consistently depending on the writing style and audience.
Use Numerals for Percentages:
✔ Always use numerals for percentages, even for numbers below 10.
Examples:
• Correct: Only 3% of applicants were accepted.
• Correct: Sales increased by 9% this quarter.
✔ Use the percent sign (%) in business and scientific writing but spell out “percent” in formal academic writing.
Examples:
• Business/Scientific Writing: Market share increased by 12% last year.
• Academic Writing: Only twelve percent of respondents agreed with the statement.
✔ In formal writing, avoid starting sentences with a numeral percentage—either rephrase or spell it out.
Examples:
• Incorrect: 75% of employees support the new policy.
• Correct: Seventy-five percent of employees support the new policy.
• Better Alternative: The majority (75%) of employees support the new policy.
✔ For decimal percentages, use a leading zero for values less than 1.
Examples:
• Correct: The error rate was 0.8%.
• Incorrect: The error rate was .8%.
4. Decimal Numbers and Fractions
Decimals and fractions should be formatted according to context and readability.
✔ Use numerals for decimals and keep them consistent.
Examples:
• Correct: The solution contains 2.5 grams of sodium.
• Correct: The GDP growth rate was 3.75% last year.
✔ Use words for simple fractions in general text, but numerals in scientific contexts.
Examples:
• General Writing: About one-third of respondents agreed.
• Scientific Writing: The compound contained 1/3 of its original mass.
5. Currency and Units of Measurement
✔ Use numerals for currency and always include the appropriate symbol or abbreviation.
Examples:
• Correct: The total cost was $5,250.
• Correct: The research grant awarded €1.2 million to the university.
✔ Use numerals for measurements (weight, height, temperature, etc.) in technical writing.
Examples:
• Correct: The sample was stored at -20°C.
• Correct: The package weighs 2.5 kg.
✔ For non-technical writing, spell out simple measurements when readability is a concern.
Example:
• Correct: The property spans five acres.
6. Number Ranges and Dates
✔ Use an en dash (–) for number ranges instead of a hyphen (-).
Examples:
• Correct: Pages 45–60 contain additional references.
• Correct: The study analyzed data from 2001–2015.
✔ For dates, do not use ordinal numbers (st, nd, rd, th) in professional writing.
Examples:
• Correct: The meeting is on March 15, 2024.
• Incorrect: The meeting is on March 15th, 2024.
✔ When writing decades, use numerals without an apostrophe.
Examples:
• Correct: The economy grew rapidly in the 1990s.
• Incorrect: The economy grew rapidly in the 1990’s.
Final Best Practices for Formatting Numbers and Percentages
✅ Follow your style guide (APA, MLA, Chicago) for number formatting rules.
✅ Be consistent with numerals and spelling throughout your document.
✅ Use commas for large numbers to improve readability.
✅ Avoid unnecessary decimals (use 5 instead of 5.0 unless precision is needed).
✅ Write out numbers at the start of a sentence for clarity.
Proper number formatting enhances clarity, professionalism, and readability in business and academic documents.
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