bao nhiêu vs mấy — How Many (Large vs Small)

Quick Answer

Both bao nhiêu and mấy translate to "how many" or "how much" in English, but Vietnamese speakers choose between them based on the expected size of the answer. Use mấy when you expect a small number (roughly 1–9), and use bao nhiêu when the number could be large, unknown, or when asking about prices and quantities in general.

Getting this wrong is not a serious error — native speakers will still understand you — but choosing correctly makes your Vietnamese sound much more natural.

Comparison Table

Detailed Explanation

When to use mấy

Use mấy when you genuinely expect the answer to be a small, single-digit number. This is common when asking about people in a family, floors in a building, items on a small list, or years of study. The implied assumption is that the number is manageable and countable on one hand.

For example, if you ask a friend how many siblings they have, you use mấy — because families typically have a handful of children, not hundreds. If you ask how many languages someone speaks, again mấy is natural.

Structurally, mấy is placed directly before a classifier and noun: mấy + classifier + noun. For example: mấy cái (how many things), mấy người (how many people), mấy con (how many animals).

When to use bao nhiêu

Use bao nhiêu when the number could be large, when you genuinely have no idea what range to expect, or whenever you are asking about prices, money, weight, distance, or time duration. Think of it as the "open-ended" version.

Asking how many students are in a school? Use bao nhiêu — the answer could be hundreds or thousands. Asking the price of something at the market? Always bao nhiêu. Asking someone's age when you truly don't know? Bao nhiêu tuổi is the polite, standard form.

Unlike mấy, bao nhiêu can be used without a classifier: bao nhiêu tiền (how much money), bao nhiêu ki-lô-gam (how many kilograms). When used with count nouns it can optionally take a classifier, but often omits it.

Age — a special case

For asking age, both words are used but with different social registers. Bạn bao nhiêu tuổi? is the standard, polite form. Bạn mấy tuổi? is more casual and is often used with children or close friends. When speaking to elders or in formal situations, always use bao nhiêu tuổi.

Note for Hán-Việt learners (JA/ZH/KO)

Bao nhiêu comes from the Sino-Vietnamese root bao (包/飽, originally meaning "to contain" or "how much") combined with nhiêu (饒, meaning "abundant, plentiful"). Japanese and Chinese learners may recognize the concept of 幾つ (ikutsu) vs 何個 (nanko) in Japanese, or 几个 (jǐ gè) vs 多少 (duōshǎo) in Chinese — this is a very similar small-vs-open distinction. Korean learners can compare 몇 (myeot) for small expected numbers vs 얼마나 (eolmana) for open quantities.

Example Pairs

The following pairs show the same or similar context using both words, so you can feel the difference in expectation.

Common Patterns

The following fixed patterns always use one specific word. Memorizing these will help you sound natural immediately.

Important: For telling or asking the time, Vietnamese always uses mấy giờ — never bao nhiêu giờ. This is a fixed, idiomatic expression you should memorize as a chunk.

Common Mistakes

Mistake 1 — Using mấy to ask about prices

Learners sometimes use mấy when asking how much something costs, perhaps by analogy with "how many coins/dong." However, Vietnamese always uses bao nhiêu for prices and money.

❌ Cái này mấy tiền?

✅ Cái này bao nhiêu tiền?

Prices are considered open-ended quantities — they could be any amount — so bao nhiêu is always required. The phrase bao nhiêu tiền is a fixed chunk that every Vietnamese learner should memorize early on.

Mistake 2 — Using bao nhiêu giờ to ask the time

Because bao nhiêu is the "general" word, learners assume it works for asking the time. But "what time is it" is a fixed expression in Vietnamese that uses mấy.

❌ Bây giờ là bao nhiêu giờ?

✅ Bây giờ là mấy giờ?

The reasoning is that clock hours run from 1 to 12 (or 24) — always a small number — so mấy giờ is the natural and idiomatic choice. This is one of the most common errors among beginner learners.

Mistake 3 — Using mấy for large populations or quantities

When asking about large quantities such as city populations, the number of products in a store, or the size of an audience, learners sometimes still reach for mấy because it feels simpler. This sounds unnatural to native speakers.

❌ Thành phố Hà Nội có mấy người?

✅ Thành phố Hà Nội có bao nhiêu người?

When the answer could realistically be in the thousands or millions, mấy is inappropriate because it implies a small expected value. Switch to bao nhiêu any time the quantity is large or genuinely unknown.

Mistake 4 — Forgetting the classifier with mấy

Mấy almost always requires a classifier between itself and the noun, just like other Vietnamese quantity words. Dropping the classifier is a common beginner slip.

❌ Bạn có mấy sách?

✅ Bạn có mấy cuốn sách?

Here cuốn is the classifier for books. With bao nhiêu, the classifier is optional in many cases, but with mấy it is almost always required. When in doubt, include the classifier.

Related Grammar Points

• gì vs nào — What vs Which (Comparison A1)
• là vs Zero Copula — When to Use 'là' (Comparison A1)
• không vs chưa — Two Types of Negation (Comparison A1)
• đã vs rồi — Past Tense vs Completion (Comparison A1)
• cái vs con — Object vs Animal Classifiers (Comparison A1)
• nào — Which? in Vietnamese (Grammar A1)

Quick Quiz

Fill in the blank with mấy or bao nhiêu:

1. Xin lỗi, cái túi này _____ tiền?

Hint: You are asking about the price of a bag at a shop.

2. Bây giờ là _____ giờ rồi?

Hint: You want to know what time it is right now.

3. Thư viện trường bạn có _____ cuốn sách?

Hint: You are asking about the total number of books in a university library.