one book two cars first day Numbers function as determiners before nouns. Handling numbers in writing can feel like a minefield of "should I spell it out or use digits?" While style guides (like APA, MLA, or Chicago) have their own quirks, there are some universal ground rules that will keep your writing professional and polished.
The "Rule of Ten"
Most styles follow a simple threshold to decide between words and numerals:
Zero through nine: Spell them out (one, five, nine).
10 and above: Use numerals (12, 50, 1,000).
Pro Tip: If you have a list of numbers in the same sentence, be consistent. Instead of saying "I have 5 apples and twelve oranges," use "5 apples and 12 oranges."
4 Golden Rules of Number Grammar
1. Never Start a Sentence with a Numeral
Even if the number is large, you must spell it out if it begins the sentence.
Wrong: 500 people attended the gala.
Right: Five hundred people attended the gala.
Better: A total of 500 people attended the gala. (Rearranging is often easier!)
2. Hyphenating Compound Numbers
When spelling out numbers from twenty-one through ninety-nine, always use a hyphen. This also applies when these numbers are part of larger numbers (e.g., two hundred twenty-five).
3. Ordinal Numbers (Order)
The same "Rule of Ten" usually applies here:
Spell out: First, second, ninth.
Numerals: 10th, 21st, 50th.
Note: Avoid using superscripts (10
th
) in formal business writing unless specifically requested; "10th" is cleaner.
4. Percentages and Decimals
In technical or scientific writing, always use numerals for percentages and decimals.
Correct: The ROI increased by 5%.
Correct: The solution was 0.75 liters.
Grammar Note: In formal prose, some prefer "5 percent" over the "%" symbol, but the numeral stays.
When to ALWAYS Use Numerals
Regardless of how small the number is, use digits for:
Addresses: 5 Maple St.
Dates: March 4, 2026.
Exact Sums of Money: $5.50 or $7 million.
Time: 8:00 a.m. (Unless using "o'clock," then spell it: "eight o'clock").
Ages: He is 7 years old (though some literary styles still spell this out).
Common Confusion: Numbers as Adjectives
When a number and a unit of measurement act as a single adjective before a noun, use hyphens:
A ten-minute walk.
A five-mile run.
A 12-story building.