Less Versus Fewer

These two words are often mixed up in usage. Especially by us Indians.

But there are distinct contexts where each is used/not used.

How do you decide which to use when?

It's simple: use fewer when you're talking about things you can count, and less when you're talking about things you cannot count.

Let's get to the details... 

You use "fewer" when you are talking about people or things in the plural form. E.g. Dogs, schools, cars.

Examples

1. Fewer students are opting to study this course.
2. Fewer than 100 dogs die each year of cancer.

You use "less" when you're talking about something that can't be counted. E.g. Water, music, homework.

Examples

1. When I'm at work, I listen to less music.
2. The pond has less water.

Exceptions

As is the case with most English grammar rules, there are exceptions to this one.

For the following, you need to use "less" instead of "fewer", even though you can quantify them:

• Time
• Distance
• Money
• Weight

Examples

Here are some examples using "less" for these exceptions:

• I have less than 2 hours to finish this work
• The library is less than 5 KMS from here
• I have less than ₹50,000 in my bank account
• I'm sure the dog weighs less than 5 KGS.

This is because they're treated as singular:

• 6 hours is too long a time to spend driving
• 500 KMS is too taxing to drive
• ₹ 50,000 is a lot of money
• My weight is 60 KGS

TL;DR

Use

• "Fewer" when referring to people or things in plural
• "Less" for the uncountable - water, music, work
• "Less" when talking about time, distance, money, weight--exception to the general rule