When to Use Less Versus Fewer

This month’s post focuses on two terms that are often swapped: less and fewer. Don’t they mean the same thing? Essentially, yes—both terms involve a smaller number or limited amount of whatever thing you’re discussing. So how do you know when to use each term? Here’s the easiest, most straightforward way. 

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In general, use “fewer” with things you can count (like medications, symptoms, and Qbank questions) and “less” with things you can’t count (like amounts and mass nouns, such as food and water). Here are some examples:

I completed fewer AANP practice questions last night than I did the night before.

AANP practice questions are countable—you know how many of them you have, so use “fewer.”

He drank less water before his surgery shelf exam.

Water isn’t countable—it’s an amount, so you should use “less.”

That’s simple enough. But what about things we measure?

The lesions are [less/fewer] than 3 cm in diameter.

Technically, centimeters are countable. So shouldn’t we use “fewer”? No. This is an exception (English is complicated!). Measurements (e.g., time, distance, money) typically use “less.” 

The lesions are less than 3 cm in diameter.

Your turn! Try this one:

The hospital has just purchased a new proton beam purported to deliver targeted radiation with [less/fewer] side effects than traditional radiation therapy.

Side effects are countable—use “fewer.”

The hospital has just purchased a new proton beam purported to deliver targeted radiation with fewer side effects than traditional radiation therapy.

How about this one?

She developed painful erythematous macules with purpuric centers on her face and trunk covering [less/fewer] than 10% of total body surface area.

Percentages aren’t countable—use “less.”

She developed painful erythematous macules with purpuric centers on her face and trunk covering less than 10% of total body surface area.

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Keep it simple for yourself: if you can count the thing you’re discussing use “fewer.” If you can’t count it or if it’s a measurement, use “less.”