N4
そんなに
So (much), That much, Like that
そんなに暑いと思うならエアコンをつければいい。
If you think it's that hot, you should turn on the air conditioner.
Explanation
「そんなに」 has 2 uses
1Not that …
With a negative: not as much as you might think: 「そんなに難しくない」 it's not that hard.
もうお金がそんなにないから、買うのをやめましょう。
Because I don't have that much money, I won't buy it.
そんなに迷惑をかけたと思っていなかったです。すみませんでした。
I didn't realise I'd caused you that much trouble. I'm sorry.
2That much
Points to the degree the other person shows, often with surprise or to hold them back: 「そんなに怒らないで」 don't get so angry.
このケーキはそんなに甘いんですか。
Is this cake really that sweet?
そんなに暑いと思うならエアコンをつければいい。
If you think it's that hot, you should turn on the air conditioner.