The thing about teenagers and food, but especially something as delicious as lasagna, is they eat just about twice as much as older adults; you get about 6 servings from a 9x13 pan- maybe 8 if there are a lot of girls- and some of the kids will eat 2 servings.

So take your recipe for one 9x13 pan and multiply the sauce requirement times 25 or 30; this will give you the number of cups; divide by 16 for the number of gallons.

Suggestions- 1) Consider making some pans meatless, if your daughter's friends are typical teens, a portion of then will be active vegetarians and/or dieting. With this much lasagna, you may even want to make some with an alfredo style white sauce, instead of all marinara 2)If you have lots of hot garlic bread, they will eat somewhat less lasagna. 3) Plan how you are going to get it all heated up, and remember you can make 18 quart Nesco roasters or big Hamilton Beach roasters full of lasagna, then both cook it and keep it warm right in the roaster (9x13 pan is 2-3 quarts, depending on how thick you make your lasagna). These look like portable steam table trays full, very handy too.

Mostly adults will allow you to cut 12 or 15 servings to the pan, depends on what else you are serving.

A Lemon or lime sherbet dessert, or other fruit sherbet or sorbet, is very good with lasagna. A little drizzle of rasberry syrup makes it extra pretty and tasty.