A lot of recipes I see call for lemon quantity but this can be very relative as some lemons differ in weight/size, thus yielding to different amounts of lemon juice.
For instance, if I wanted to make half a gallon's worth of lemonade, what would be the recommended ratio of lemon juice to water be? I tend to use about 2 cups of sugar to give you an idea of level of sweetness in half a gallon's worth of lemonade.