5'4, 125lbs and M is perfect. Waist falls exactly as it should, straps too. Length is great, inseam - all of it fits correctly. Lightweight and comfortable and really great for warm-up. I am very happy with this and definitely recommend it.
I am 5'4", 103 pounds, and got a small.
It's a bit short and stops about 3 inches above my ankle bones. It's a loose fit, but medium could have been better. But then again, the top part fits perfectly, so I can't say for sure.
Other than that, I love this warm up! You can roll up, down, and use the whole or some part(s) of it.