I doubt you have much leg fat. But squeezing the tissue between your fingers will tell you. Fat feels soft and jiggly, muscle feels stiffer and more fibrous.
The fat is mostly just under your skin (felt by poking with a finger), and muscle is under that (felt by pulling your loose skin tight with one hand and poking deeply with a finger).
Plus, fat cannot contract on command; extending your knee while holding your leg out in front of you will reveal bunched tissue near your knee that feels hard to the touch. Bending your knee, pulling your heel forcefully up toward your ass will make the back of your leg (hamstring) bunch up and harden.