How do you say it is so hot outside in french?

There are a few ways to say "it is so hot outside" in French, depending on the level of intensity you want to convey:

Formal:

* Il fait très chaud dehors. (It's very hot outside.)

* Il fait une chaleur étouffante. (It's stifling hot.)

Informal:

* Il fait une chaleur de fou! (It's crazy hot!)

* Il fait un temps de chien! (It's dog-eat-dog weather! - This expression implies it's unpleasant and hot.)

* J'ai trop chaud! (I'm too hot!)

More descriptive:

* Le soleil tape fort. (The sun is beating down hard.)

* L'air est lourd et moite. (The air is heavy and humid.)

The best way to say it depends on the context and your personal preference.