How to measure an outseam on a skirt?

Knowing Tilly's its probably too short. Have your mom draw a line on your leg where your fingertips stop. Then measure from your waist (hip hugger style probly) to that point. The only thing I can think of is to go ahead and buy them then return them if they don't work, or just wear em for fun. Another thing thats in style now, is ripped out unfinished seams. So if ripping out the seam makes em long enough, maybe you could do that. Good luck.