多久 vs 多长时间 (duōjiǔ vs duō cháng shíjiān): how to ask “how long”
Both 多久 and 多长时间 mean “how long” and are used to ask about duration. They are near-synonyms, but 多久 is more colloquial and compact, while 多长时间 is slightly more formal or explicit. In most everyday situations, they are interchangeable, but 多久 is more common in casual speech and with verbs like 等 (wait) or 住 (stay).
多久 and 多长时间 both ask about the length of time an action lasts. 多久 is a single word (多久) that inherently means “how long,” while 多长时间 is a phrase literally meaning “how long a time.” 多久 is generally more casual and is the default in spoken Chinese, especially with common verbs like 等 (wait), 住 (stay), or 学 (study). 多长时间 is slightly more formal and can be used for emphasis or in more deliberate questions. In most contexts, they are interchangeable without a change in meaning, but learners often overuse 多长时间 because it feels more transparent, while native speakers prefer 多久 in everyday conversation.
When to use each
Use 多久 in informal, everyday questions about duration. It is the more common and natural choice, especially with verbs like 等 (wait), 住 (stay), 学 (study), or 做 (do). It works well in short, direct questions like '你等多久了?' (How long have you been waiting?).
多久 can also be used in affirmative answers like '不久' (not long) or '很久' (a long time). It is rarely used in formal writing.
Use 多长时间 when you want to be more explicit or slightly formal about asking duration. It is common in written Chinese, polite questions, or when the duration is emphasized. For example, '你要多长时间才能完成?' (How long will it take you to finish?). It is also preferred in longer, more complex sentences.
The 长 (cháng, 'long') in 多长时间 makes it more literal, so it can feel more analytical. In very casual speech, 多久 is usually preferred, but 多长时间 is never wrong.
At a glance
| 多久 | 多长时间 | |
|---|---|---|
| Register | Colloquial / everyday speech | More formal / explicit |
| Structure | Single word (多久) | Phrase (多 + 长 + 时间) |
| Common use with verbs | Frequent with 等, 住, 学, 做 | Frequent with 花 (spend time), 需要 (need), 完成 (finish) |
| Typical reply | 不久 / 很久 | 不太长时间 / 很长时间 |
Examples
- 多久你等多久了？Nǐ děng duōjiǔ le?How long have you been waiting?Natural everyday use with 等 (wait).
- 多长时间你等多长时间了？Nǐ děng duō cháng shíjiān le?How long have you been waiting?Slightly more formal; still correct but less common in casual speech.
- 多久你来北京多久了？Nǐ lái Běijīng duōjiǔ le?How long have you been in Beijing?Typical question with a location verb.
- 多长时间这个项目需要多长时间？Zhège xiàngmù xūyào duō cháng shíjiān?How long does this project need?Formal context with 需要 (need) – 多久 would also work but feels less precise.
- 多久他学了多久汉语？Tā xué le duōjiǔ Hànyǔ?How long has he studied Chinese?Colloquial with 学 (study).
- 多长时间你每天锻炼多长时间？Nǐ měitiān duànliàn duō cháng shíjiān?How long do you exercise every day?Routine question – both acceptable, but 多长时间 sounds more deliberate.
Common mistakes
- Using 多长时间 when a native speaker would naturally say 多久 in casual conversation (e.g., '你等多久了？' not '你等多长时间了？' unless emphasis is needed).
- Thinking 多久 cannot be used in formal contexts – it can, but 多长时间 is safer in writing.
- Confusing 多久 (duration) with 多长 (how long in space, e.g., length of a table). '这条路多长？' asks length, not time.
- Omitting 了 (le) when asking about duration up to now: '你等多久？' (without 了) means 'How long will you wait?' (future), not present perfect.
FAQ
- When do I use 多久 vs 多长时间?
- In most everyday spoken situations, use 多久 – it’s short and natural. Use 多长时间 when you want to sound a bit more formal or explicit, such as in writing or when you want to emphasize the duration. They are largely interchangeable, so you can use either without causing confusion.
- Can I use 多久 and 多长时间 in the same sentence?
- No, you should choose one. Using both in the same question would be redundant, e.g., '你等多久多长时间了？' is incorrect.
- Is there a difference in the answer structure?
- Not really. Both can be answered with specific time expressions (e.g., 两个小时, 三天) or general ones (e.g., 不久, 很久 for 多久; 不太长时间, 很长时间 for 多长时间). However, 多久 is more common with 不久 and 很久 in answers.
- Does 多久 always imply a long time?
- No. 多久 is neutral – it can ask about any length of time. The '久' character means 'long (time),' but in questions, it functions like 'how long' without presupposing a long duration. For example, '你等多久了？' can be answered with '五分钟' (five minutes).