Do I use amount or number?

A common mistake is writing amount when you mean number and vice versa. So, what is the difference between the two? When you check amount and number in the dictionary, they look like they could mean the same thing. You won't repeat this mistake once you know the rule.

Amount

According to the Oxford English Dictionary, amount has five different meanings, but the two below are the ones we'll focus on.

1. Chiefly followed by of and a plural noun. A number of people or things; spec. (esp. in early use) a total number, the sum total.

2. Chiefly followed by of and a mass noun. A quantity of something; a portion or measure; spec. (esp. in early use) the total or full quantity.

You should use amount when the thing you are referring to is uncountable.

You can say

The amount of water in the pond has increased exponentially this winter

Because water in the pond is not countable.

The amount of water in the pond has increased exponentially this winter

Number

According to the Oxford English dictionary, number is:

1. The precise sum or aggregate of a collection of individual things or persons; the quantity or amount.

You should use number when the thing you are referring to is countable.

You can say

I couldn't be happier; the number of books I sold last month exceeded two hundred copies

Because book sales are countable.

I couldn't be happier; the number of books I sold last month exceeded two hundred copies

Conclusion

Think: can I count [whatever you are talking about]?

If the answer is yes, use number. If the answer is no, use amount. And remember, practice makes perfect.

Source: Oxford English Dictionary