How much punch do I need to make for a wedding reception of 150 guests?

We are having a dinner at the reception, with tea, coffee, and water I believe, and needed to make punch. Do I need to wait to make the punch until after the dinner when it is time for cake? I am making a simple punch using lime sherbet and lemon-lime soda, I know the ratio is 2/1, soda/sherbet, but I have no idea how much I should be buying for a party this size. Any help is greatly appreciated.|||If everyone at your party had just two cups that's nearly 19 gallons of fruit punch! That's about 35 two liters of soda plus sherbet. Of course with tea/water/coffee it's possible that punch would only need half of that or so. A cup of punch really isn't all that much so I would venture to say that each person would average out to be 2-3 cups. And if children are attending that's all they will be drinking. :) (With an average of 3 cups of punch per person you would need 28 gallons, or 53 2-liters of soda.)|||well there's 8 and a half cups or almost 68 ounces in a 2 liter. Well thats about 3 people to a 2 liter soda . That's 50 2 liter for just one drink of punch but thats not counting the sherbet . But you also said your having tea and coffee and water but it also depends on where your having it and when . I live in Florida so it is hotter so alot of people would drink colder drinks . Also same for winter and in summer.