The amount of VS The number of, etc

Is it OK to use the amount of with countable nouns? I have come across the usage of it with people, but I am confused whether to use it with countables.

What about the proportion of? How different is it from the amount of and the number of ?

Thank you in advance for the answer.

Solution 1:

This question appears to arise from a comment I made in an earlier question.

Op had written:

The pie charts compare the amount of people enrolled on six courses, … in a certain college in the UK.

I had commented:

We would not normally say "amount of people" - either number of people (if you are showing actual numbers) or proportion of people (if using, say, percentages). amount is used for 'non-discrete' items (i.e. things that you cannot count, but can only measure e.g. by weight or volume, such as sugar or a liquid.

OP is now asking about the usage of amount is a sentence such as:

The number of people commuting by bus considerably increased in the year of 2013.

and asks whether amount or proportion could replace number.

Cambridge Dictionary defines amount as follows and includes a Grammar Note:

amount
noun [countable]
a collection or mass, especially of something that cannot be counted: [example sentences omitted - see link]

Grammar
Amount of or number of?
We use amount of with uncountable nouns. Number of is used with countable nouns:

• We use a huge amount of paper in the office every day.
• The amount of time it took to finish the job was very frustrating.
• A great number of students volunteer each year for environmental projects.
• Not: A great amount of students volunteer …
• I have a number of things I want to talk to you about.

The original sentence refers to "[comparing] the amount of people enrolled on six courses [using a pie chart]". The context clearly suggests that the actual numbers of student involved are known. In that instance, it seems that number or proportion (depending on the values actually shown in the pie chart) would be appropriate; and that amount would, at best, be non-idiomatic. That view is reinforces by the Grammar Note above indicating that "A great amount of students volunteer …" would be wrong.

In the second example sentence:

• amount may be more acceptable because there is (presumably) no reference to precise numbers;
• even so, number still sounds more idiomatic to me; and would refer to the overall (estimated) number of bus commuters using buses;
• proportion would be appropriate only if there were a comparison with (for example) the overall number of commuters.

But beware: in this case the difference between number and proportion could be important, because one value could go up while the other value goes down. For example:
- Year 1: 4 million commuters use the bus; 6 million use the train; hence 40% (of the total 10 million) use the bus.
- Year 5: 5 million commuters use the bus; 8 million use the train; hence 38.5% (of the total 13 million) use the bus.
Thus the number of bus commuters has increased by 1 million (23%), but the proportion of bus commuters has decreased by 1.5%.

Solution 2:

The proportion would refer to the percentage with reference to a larger total.

If you refer to the amount of people without quantifying them exactly, this would be okay as a group of "people" may be undefined and uncounted. However if you counted them, then the number of people sounds better.

The proportion of people who responded to the letter. The amount of people using the facilities. The number of people/persons on the train exceeded the safe limit of 500.

Solution 3:

Grammarist has a balanced article dealing with the subtle 'tacit massification' of count nouns that occurs in situations like this.

Amount vs. number

Amount is used in reference to mass nouns (i.e., uncountable nouns such as bravery, water, and charisma). Number is used in reference to count nouns (i.e., countable nouns such as dog, year, and eyeball).

For example, because the noun person can be counted, the phrase amount of people might be considered incorrect. The distinction tends to weaken, however, when we’re talking about great numbers. The amount of people in the room would sound wrong to many careful speakers of English, while the amount of people in China would not seem so glaringly wrong (though many English-speakers would still consider it questionable). In any case, it’s always safer to use number in situations like this.

It's really a metaphorical usage, considering countable elements as an amorphous whole. 'The volume of people' is a slightly different metaphorical usage, but is quite a common usage.

...

Proportion is used with both count- and non-count situations (the proportion of left-handed pupils in the class; the proportion of ethanol in the sample).