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.
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).
I will take a week off.
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.
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.
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
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.
I'll be back in one week.
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.
毎週金曜日に会議があります。
There's a meeting every Friday.