“On a scale of one to five, I'd give it a four.”
You went to watch a movie last weekend. You're talking about it with a friend, who asks what you thought of the movie. You liked it quite a bit, so you rate it this way.
On a scale of one to five, I'd give it a four.
When people give something a number rating, they usually have an idea of what the top possible rating is. For example, you might rate something a "6" with the idea that the top possible rating is "10". That top value defines the "scale" of the rating. So you can say:
I'd rate it 6 on a scale of 10.
On a scale of 1 to 10, I'd rate it a 6.
The most common scales are one to three, one to four, one to five, one to 10, and one to 100.
When you're rating how good something is, you can say what rating, grade, or score you "would give" it:
I'd give it a three out of ten.
I'd give it a B+.
I'd give it two stars.
Why do we use "would" in this expression? Imagine that part of the sentence is left out:
I'd give it a three out of five (if I were rating it formally).