time / time period+ 一次 is used for describing frequency, it means "once" or "one time". for example, 我每星期去一次超市。 我每天喝一次咖啡。 ——你多长时间/多久洗一次衣服？ ——我三天洗一次衣服。 So we can also say "两次"、“三次”、。。。 For example 我每星期去两次超市。 我每天喝三次咖啡。 Hope this will be helpful. : ) Li Ying

一次 means one times As the question in english is how often do you go to restaurant at one times.but I think that it would be wired if one time is used in question of english version As the answer of this quesion in english, I think that it is I go to restaurant quite often about one time per week.

That means "a session of". The literal translation is this though in English we don't structurea questionlike that: How often do you have a session at the restaurant? 你多久做一次爱? (Literally, How often do you have a sex session?) 你多长时间剪一次发? (Literally, How often do you have a hair-cut session?) It is the Chinese structure for asking about frequency. "多久一次…" "How often do you have a session of…"

Haha, you asked a very good question. Try to understand in Chinese question, we use 一次 to avoid confusion. otherwise it will be 你多长时间下馆子? -If you translation it into English, coud be how long you will stay in the restaurant? or when you will go to restaurant?