英语恰到好处怎么说怎么写

"Just right" or "just the right amount" are both good ways to describe something that is "恰到好处" in Engpsh.

For example:

The temperature outside is just right - not too hot or too cold.
This piece of music is just the right amount of energetic - not too fast or too slow.

Alternatively, you could also use the phrase "perfectly balanced" to describe something that is "恰到好处". For example:

The flavors in this dish are perfectly balanced - not too spicy or too bland.
The difficulty level of this puzzle is perfectly balanced - not too easy or too hard.