I used a lg on my 18-20 lb ds over his HUGE nighttime diaper so they definitely run big. As a comparison, the lg Litewrap is considerably bigger than the XL Bumpy wool we sometimes use. I personally loved the fit, nice tall rise which is what we need. But it was never leakproof for us. I tried "sealing" it in the dryer and cared for it exactly like all my other PUL so I'm not sure what the problem was. I got it new and it leaked every time. I only used it at night though and have a heavy wetting tummy sleeping boy, so there's a lot of wetness and pressure right up front. But every other cover I have is more reliable than the Litewrap. I might have been happy with it if I used it as a daytime cover.