Two formats dominate how we write “one and a half” in regular sentences: either as a hyphenated compound (one-and-a-half) or as three separate words (one and a half). Both versions are perfectly acceptable now—modern style guides don’t flag either as wrong. Need something more precise? Use the decimal 1.5 (the go-to in technical writing) or the mixed number 1½.
Quick Fix Summary
Go with either one-and-a-half (hyphenated) or one and a half (three words) in running text. For technical work, use 1½ or 1.5. Skip the hyphen when the phrase follows the noun it modifies (e.g., a one-and-a-half-year project or a one and a half year project).
What’s going on here?
“One and a half” sits somewhere between a plain number and a unit of measure. Old grammar rules demanded a hyphen when the phrase acted as a compound modifier before a noun, but today’s major style guides (Chicago, APA, AP) accept both hyphenated and unhyphenated versions without complaint. When you’re dealing with numbers or symbols, both 1½ and 1.5 are perfectly fine.
Here’s how to nail it every time
- Pick your format
- In regular sentences: one and a half (three words) or one-and-a-half (hyphenated)
- In technical or financial writing: 1½ or 1.5
- Handle hyphens the right way
- Before a noun: a one-and-a-half-hour drive or a one and a half hour drive
- After a noun: The drive lasted one and a half hours (no hyphen in sight)
- Switch to decimals or fractions for tables and graphs
- Decimal: 1.5 hours
- Fraction: 1½ hours
Still stuck?
- Default to decimals in formal papers – 1.5 removes any style-guide guesswork.
- Let a style checker do the heavy lifting – Microsoft Word’s Editor pane or the free Grammarly add-in can catch inconsistent hyphens and suggest the version your guide prefers.
- Check the publisher’s style guide – journals and companies often spell out their own hyphenation rules, so follow theirs if you’re submitting somewhere specific.
Keep it consistent next time
- Choose one version (one-and-a-half or one and a half) and stick with it throughout your document.
- Lean on Word’s built-in styles or a custom template to keep punctuation uniform.
- When in doubt, fall back on 1.5—it’s never unclear.
- Same rule applies to “a half” on its own: a half or a-half works fine.
