I believe it's a size medium (800-1100 lbs) but my horse has a very thick head and neck and although I can zip it up, it's uncomfortably tight in the face. I think it would fit most horses in the stated weight range, and I can measure my horse's face for comparison if needed.
I paid $38 for it new, will sell for $20 including USPS Priority shipping within the U.S.
It's only been on my horse 3 times for maybe 5-10 minutes each time (surprise, surprise, each time it still didn't fit!) It's in like new condition, but has been washed and there are still a couple white hairs on it here and there.