Knowing bao nhiêu tiền? (“How much money?”) is useful, but it does not solve every quantity question. Sometimes a speaker wants a small count. Sometimes they want an amount, an unknown-sized collection or a duration. Sometimes moving mấy changes the question from “which date?” to “how many days?”
The practical task is to identify the answer you need before selecting the question. Mấy often accompanies an expected relatively small count. Bao nhiêu is broader, including amounts and counts whose size is not assumed to be small. The noun and its position then tell the listener what kind of number to give.
The counts, dates and prices here are invented learning facts. Personal questions address fictional adult peers as bạn. The lesson is general Vietnamese, not a claim that Southern speakers apply a separate arithmetic rule.
An expectation is not a hard numerical limit
Bạn có mấy cuốn sách? How many books do you have?
This can fit an ordinary question about a small set of books in someone’s bag. Bạn có bao nhiêu cuốn sách? asks how many books they have without that small-count framing.
MSU’s quantity lesson describes the difference as an expectation, often a small number for mấy. Treating it as a rule that a reply must be below ten would confuse the speaker’s expectation with the actual answer. If the bag contains twelve books, the truthful count does not change to accommodate your question.
Both questions retain cuốn sách, the counted object. That matters. A number alone could be a count of books, a page number or a price. Your noun expression tells the listener which.
An original exchange:
Minh: Bạn có bao nhiêu cuốn sách? How many books do you have?
Lan: Tôi có mười hai cuốn. I have twelve.
The short answer retains the unit cuốn, because the book noun is already understood. It does not claim that cuốn is the right counting expression for every object.
Amount questions need the relevant measure
Cái bút này bao nhiêu tiền? How much does this pen cost?
Hai mươi nghìn đồng. Twenty thousand đồng.
That is an invented price for the exercise, not a quote from a Vietnamese shop. Tiền makes the requested amount money. TUFS’s price-question module documents fuller and shortened bao nhiêu price frames.
Now ask about time remaining:
Còn bao nhiêu phút? How many minutes are left?
The question requests a duration measured in minutes. It does not ask for the clock time. PNE’s classroom expressions show remaining-time questions and answers.
Mấy giờ?, by contrast, is an established way to ask for a clock time. Do not use the small-count guideline to reject it when the answer names eleven o’clock. The phrase does a time-identification job in its own construction.
Date versus duration is a word-order problem
Compare:
- Bạn ở đây mấy ngày? How many days are you staying here?
- Bạn đi ngày mấy? What date are you leaving?
In mấy ngày, the question word precedes the unit and asks for a number of days. In ngày mấy, it follows the time noun and asks for the date. MSU’s date lesson also contrasts bao nhiêu năm (“how many years”) with năm bao nhiêu (“which year”).
For a learner, this is more immediately useful than a long inventory of number-related phrases. It separates two answers that cannot substitute for one another: “three days” and “the third of the month.”
An original answer-type worksheet
Use these fictional facts:
- A bag contains three notebooks
- A shelf collection contains twelve books
- A pen costs twenty thousand đồng
- A stay lasts four days
- A departure is on the twenty-third of the month
- A break begins at eleven o’clock
For each fact, write a question that asks for the number without giving it away. For the collection, use the broader bao nhiêu wording. For the bag, practice mấy.
One answer set, with the reason
- Trong túi có mấy cuốn vở? How many notebooks are in the bag? The exercise presents a small count of bound notebooks.
- Trên kệ có bao nhiêu cuốn sách? How many books are on the shelf? The broader wording asks for the size of the shelf collection.
- Cái bút này bao nhiêu tiền? How much does this pen cost? The answer is a money amount, not an item count.
- Bạn ở đây mấy ngày? How many days are you staying here? The answer is a duration.
- Bạn đi ngày mấy? What date are you leaving? The answer is a calendar date.
- Giờ nghỉ bắt đầu lúc mấy giờ? What time does the break begin? The answer is a clock time, not a count of hours.
A diagnostic question
If someone answers question 4 with Ngày hai mươi ba (“the twenty-third”), what went wrong? They have supplied a date where the exercise needs a duration. A clarifying Mấy ngày? focuses the missing information. Do not interpret a bare number as the correct type of answer until its unit is clear.
You can apply the same practice to your own study material: write a quantity question, then label its expected answer “count,” “amount,” “duration,” “date” or “clock time.” That label reveals more about the question’s job than a one-word translation of mấy or bao nhiêu.