You jump as high as you can from a running start of at least 10 feet.
This means you jump from your current position to a new position on the z-axis.
This is calculated:
( Creature Base Size / 1.5 ) + Body
You gaze at the towering ledge above, its craggy surface pitted and scarred. The chasm below bristles with jagged spikes. Loose pebbles scatter underfoot, the vertical gap daring your explosive, upward leap.