Although apparently "how many" and "how long” have the same meaning as, there are some criteria to differentiate them.
It uses "how long” in interrogative sentences to express “how much time”.
Ex:
How long is he going to stay in Japan? (How long will he be in Japan?)
For how long is she going to wear those crutches? (How long will she use those crutches?)
How long will she be on a diet? (How long will she be on a diet?)
How long has he been waiting for his wife? (How long has he been waiting for his wife?)
It uses "how many” in interrogative sentences to express “the amount”. However, “how many” should only be used before countable nouns.
Below are some examples of countable and uncountable nouns.
| countable nouns - countable nouns | uncountable nouns – countless nouns |
| Cups | Coffee (coffee) |
| Students (students) | Sugar (sugar) |
| eggs | Flour (wheat flour) |
| Dollars | Money (money) |
| Jar of honey | Honey |
| Sheet of paper | mustard (mustard) |
Ex:
How many students are there here today? (How many students are there today?)
How many dollars do you have on your wallet? (How many dollars do you have in your wallet?)
How many eggs is it necessary to make this cake? (How many eggs does it take to make this cake?)
How many sheets of paper does this notebook have? (How many sheets of paper does this notebook have?)
How many days are you going to stay in our house? (How many days will you stay at our house?)
Layssa Gabriela Almeida e Silva
Brazil School Collaborator
Degree in Languages - English from the State University of Goiás - UEG
Improvement course in English by Zoni Language Centers - USA - USA
English - Brazil School
Source: Brazil School - https://brasilescola.uol.com.br/ingles/how-long-ou-how-many.htm