Hold your arm out in front of you or straight out to the side parallel to the ground. That's 9 o'clock.

Straight up or down at 12 or 6 is 90 deg off level.

7:30 and 10:30 are 45 Deg off of level.

Each hour mark represents 30 degrees, half of that 15.

You can get a pretty close approximation of the angle by simply pointing your finger at the target and figuring what hour mark that angle represents.

Or go by an app or a scope

angle cosine indicator and save the math if you haven't worked up to a shooter app in the budget yet and are still working off of range/wind charts.