I just measured 2 cups of water and poured it into my 4 cup measuring pyrex cup. It was very accurate. When you fill the cup with whatever amount you want (ie 1 cup etc) you have to put it on a surface and look at it at eye level. If it is not viewed at eye-level it will not be accurate. (not the fault of the cup) When I measure my liquid, I put the cup on my window-sill at look at it right in front of my eyes. (not below or above my eye-level) I hope I have helped, but you have to look at it in the correct position. Good luck! It truly is a wonderful measuring cup.