Choosing the right word when looking at amount vs. number is an easy distinction made by looking at what it is that you are attempting to count. “Number” is used for count nouns; “amount” is used for mass nouns.
When deciding between amount vs. number, you must look at the noun to which each word applies. A count noun is something that is easily counted through some unit of measurement. Count nouns dictate the use of “number.” The number of pages in a book, for example, is easily counted, as are the number of books in a library.
A mass noun, on the other hand, is something that cannot be counted in specific measurement units or is measured in bulk. Mass nouns dictate the use of “amount.” The amount of sand on the floor is likely to be a mess to clean. In this case, “amount” is used because counting individual grains of sand is not realistic, so the sand is counted in bulk, making “amount” apply.
There are some exceptions to the general rules when looking at amount vs. number. Money, for example, is considered a mass noun when an aggregate amount is used. However, if you are counting the number of quarters in $10.00, you are using a count noun, which makes “number” appropriate.
Referring to time works the same way. If you are writing about the amount of time, you are using a mass noun. If you are writing about the number of minutes you waited, you are using a count noun.
Measuring liquids also dictates that use of amount, even if it is possible to measure the liquid in a unit of measurement, such as cups or ounces. Number is only used if the unit of measurement is used as well. You would write about the amount of milk in your glass, for example, or you would write about the number of cups in a gallon of milk.
Along with considering amount vs. number, you must make certain choices when choosing descriptive words that apply to the amount or the number of a noun. By first making the distinction on what type of noun you are dealing with, you can make the correct choice for the descriptive words found in the below list.
Apply to amount (mass nouns): little, less and much
Apply to number (countable nouns): few, fewer and many
When choosing between amount vs. number, make sure to examine the noun to which the word applies. Keeping the distinction straight is easy when you consider whether something is easily broken down into countable units or if it is measured in bulk form because individual units are either too difficult or impossible to measure.