Formula for JumpZVelocity to In-game jump height?

Any idea how to calculate the value for player’s jump height in-game? I realised that the actual amount the player jumps isn’t the JumpZVelocity; there are other things that affect it like the Gravity value.

I’m basically trying to achieve something like the image below so that I can layout my level with more precision without having to do a lot of guesswork (shift BSP/mesh, play, adjust again)