So I was playing 5e a while back, and we were ambushed by a large group of kobolds. I had to run past them taking damage from attacks of opportunity. If I could get out of their reach with a high jump that would be for the best. I wouldn't have almost cost us the match. How can you tell how high a PC can jump under normal circumstances? I know how far they can jump, but it does not explain anything about height.
The rules are on PHB p182:
When you make a high jump. you leap into the air a number of feet equal to 3 + your Strength modifier if you move at least 10 feet on foot immediately before the jump. When you make a standing high jump, you can jump only half that distance. Either way, each foot you clear on the jump costs a foot of movement. In some circumstances. your DM might allow you to make a Strength (Athletics) check to jump higher than you normally can.
Also you can add a bit of height to your horizontal jump with an Athletics check.