I always use 1 cup rice and 1 1/2 cups water with the lid on - works perfectly every time.
If you're not doing it with the lid on then you've no idea how much is evaporating (as it depends on the heat source, the pan, etc.) and therefore you have no control.
If you're not doing it with the lid on then you've no idea how much is evaporating (as it depends on the heat source, the pan, etc.) and therefore you have no control.