Typically our tshirt dresses are labeled in the listing S/M, M/L and so on. The measurements given are taken across - you would want to multiply that number by 2 and add 3-4 inches to account for stretch. Everyone has different ideas on how they would like the fit to be. Generally if it's a snug fit the dress will stretch a bit and mold to your form.

Length measurement is always taken from the shoulder seam to the hem.