In Vietnamese, we use mấy and bao nhiêu to ask about quantities, like “how many” and “how much” in English.
Asking about small numbers
If the answer is expected to be less than ten, we can (and should) use mấy (which also means “several“).
Structure
Place mấy before the measure word of a noun to ask about a small number (less than ten).
mấy + measure word + noun
When the noun is understood from context, it’s acceptable to drop it.
mấy + measure word
If the noun doesn’t have a measure word, place mấy before the noun.
mấy + noun
Examples
- mấy cái áo
how many shirts - mấy người
how many people - mấy chai nước
how many bottles of water
Asking about quantities in general
If the answer is expected to be at least ten, or unsure, we should use bao nhiêu. For example, to ask how old an adult is, you must ask bao nhiêu tuổi, not mấy tuổi.
The special usage of bao nhiêu proves useful when you don’t want to specify a measure word for the noun and leave that responsibility to the one being asked.
For example, you can simply ask bao nhiêu xoài (“how many/much mango(es)?”) and let the one being asked choose the measure word for the answer. It can be quả or trái (dialects), which is the basic measure word for “mango”, or a “container” measure word, like giỏ (“basket”) or túi (“bag”), or a unit of measurement, like cân (“kilogramme”). All options are valid. This contrasts with mấy, which needs to go with a measure word unless the noun doesn’t have one. Of course, using bao nhiêu with a measure word is still perfectly fine, but the answer must match that measure word.
Structure
The structures with bao nhiêu are similar to those with mấy. Simply replace mấy with bao nhiêu.
bao nhiêu + measure word + noun
bao nhiêu + measure word
bao nhiêu + noun
Examples
- bao nhiêu tiền
how much (money) - bao nhiêu ngày
how many days - bao nhiêu sữa
how much milk - bao nhiêu hộp sữa
how many cartons of milk - bao nhiêu lít sữa
how many litres of milk - bao nhiêu quốc gia
how many countries
Asking about dates and time
For dates and time, the principle stays the same: mấy for small numbers, and bao nhiêu if unsure.
Structure
Place mấy after thứ, tháng, or mồng to ask about days of the week, months, or “small” days, respectively.
thứ / tháng / mồng + mấy
Place bao nhiêu after ngày or năm to ask about days or years, respectively.
ngày / năm + bao nhiêu
Place mấy before giờ to ask “what time“.
mấy + giờ
Note: bao nhiêu giờ means “how many hours”, and bao giờ means “when”. The two of them and mấy giờ are three different phrases which mean three different things. Be careful not to mix them up.
Examples
Asking about ordinal numbers
For ordinal numbers, the principle stays the same: mấy for small numbers, and bao nhiêu if unsure.
Structure
Place mấy or bao nhiêu after thứ to ask “what number/position”, “how many-th”.
thứ + mấy / bao nhiêu