Rule of thumb: Use fewer if you can count it. Use less if it’s not quantifiable. The opposite of both is more.
Her diet is paying off. She weighs less than she used to, although she lost fewer kilos this month than last.
He drinks less than he used to. He had fewer beers last night than the night before.
It’s raining less than last year. Every month, there are fewer rainy days.
Fewer cars on the road mean less stress and fewer accidents.
Money, time, weight, and distance. Although you can count them, we tend to think of them as singular units.
He has less than fifty dollars in his wallet.
She has worked at our company for less than a year.
The suitcase weighed less than 20 kg, yet the airline charged me for excess baggage.
My office is less than 10 kilometres from home.
She completed her degree in less than three years.
The tricky one: Percentages
Fewer than five percent of our employees take leave between Christmas and New Year. (Employees can be counted.)
She ate less than twenty percent of her porridge and gave the rest to the dog.
Much versus many
Like less and fewer, use much for things you can’t count, and many for the ones you can.
Less means not as much. Fewer means not as many.