Translation guide
In Japanese, 'one week' is most commonly expressed as 一週間 (いっしゅうかん). The counter 週間 is used for durations of weeks, while 週 alone refers to a week as a unit of time (e.g., 'this week'). Be careful not to confuse duration with specific weeks.
一週間
one week (duration)
Expressing a period of seven days
The standard way to say 'one week' as a duration. Combines 一 (one) + 週間 (week counter).
一週間休みます。
I will take a week off.
一週間で終わります。
It will be finished in one week.
Used in some contexts, but less common than 一週間. Often appears in compounds or when the context is clear.
一週 alone can be ambiguous; 一週間 is preferred for clarity.
一週間の休暇
a one-week vacation
Referring to a particular week, not a duration
When combined with words like 今 (this) or 来 (next), 一週間 becomes part of a phrase meaning 'this one week' or 'next one week'. However, for 'this week' as a point in time, 今週 is more natural.
来週一週間、東京にいます。
I'll be in Tokyo for the whole of next week.
Means 'this week'. Note that it does not include 一 (one).
Means 'next week'.
Means 'last week'.
Expressing frequency of one time per week
Standard pattern for 'once a week'. 週 (week) + に (per) + 一回 (one time).
週に一回ジムに行きます。
I go to the gym once a week.
Means 'every week'. Implies regularity, but not necessarily exactly once.
毎週金曜日に会議があります。
There's a meeting every Friday.
週 (しゅう) is used for specific weeks (今週, 来週) or as a unit in frequency (週に一回). 週間 (しゅうかん) is a counter for duration (一週間, 二週間). Do not confuse them.
While 一週 is sometimes understood, 一週間 is the correct and natural way to express a duration of one week. Using 一週 alone may sound incomplete or literary.
一週間で戻ります。
I'll be back in one week.
処理に一週間かかります。
It takes one week to process.
今週は忙しい。
I'm busy this week.
来週会いましょう。
Let's meet next week.
先週、映画を見ました。
I watched a movie last week.