Is it "under 10 people" or "fewer than 10 people"?

A little morei

People are countable, which puts this squarely in fewer territory, not less. Under reads as a spatial word at root — under a table, under a bridge — so careful prose prefers fewer than for counts. "Under 10" is common in speech and widely understood; newsrooms split on it, but the tighter form is "fewer than 10."

The full entryii

More quick answersiii

• → When do I use "fewer"? Use fewer for things you can count: fewer chairs, fewer errors, fewer hours logged.
• → When do I use "less"? Use less for amounts you measure rather than count: less water, less noise, less patience.
• → Is it "less people" or "fewer people"? "Fewer people." People are countable, so the correct word is fewer.
• → Is it "10 items or less" or "10 items or fewer"? Grammatically, "10 items or fewer." Items are countable, so they take fewer.
• → Is it "less calories" or "fewer calories"? "Fewer calories." A calorie is a unit you can count, so the right word is fewer.