It's a matter of taste more than anything else. If they look like bell bottoms (coming down on top of the foot) instead of like harem pants gathered at the ankle, I think they are too long. If they come down straight to the gathered ankle with no blousing at all, I think they are too short. I like mine to bloom out above the gathering and curve in at the ankle so that it is obvious they are gathered. I wear mine very full in the legs so that they almost look like a skirt, and I like to use georgette or (if I am feeling rich) silk because I like the hand of these fabrics. I don't care for stiff fabrics in harem pants. Your harem pants may look very different when you make them of the costume fabric. If they are too long, you can always shorten them when you make the real things.