にするChoose an option
Use にする after a noun to choose that item from available alternatives. The alternatives may be stated directly or simply clear from the situation.
The selected option comes before the particle
Put the noun naming your choice before に. The verb する then changes for politeness and time. The construction can select a product, food, drink, destination, quantity, or another clearly available alternative.
Stated alternatives
このシャツは白と青の二色です。私は青にします。
This shirt comes in white and blue. I'll take blue.
AnalyzeThe two colors form an explicit choice set, and 青 is the selected option.
Ordering politely
The available drinks are understood from the service situation, so they do not need to be listed.
Reporting present and past choices
Change する normally: use a nonpast form for the choice you are making now and a past form for a choice already made.
Choosing something versus changing something
In the first sentence, a room is selected from possible venues. In the second, an existing room is changed into a break room; that is the separate state-change use of にする.
More examples
朝ご飯はご飯とパンのどちらにしますか。
Which will you have for breakfast, rice or bread?
Analyze私はパンにします。
I'll have bread.
Analyze席は窓側にしました。
I chose a window seat.
Analyze次の旅行先は北海道にします。
I'll choose Hokkaido as my next travel destination.
Analyzeケーキは二つにします。
I'll take two cakes.
Analyzeデザートはアイスクリームにしました。
I chose ice cream for dessert.
Analyze