: Hello!Ive been plumbing for seven years now,and I need to get my journeymens licence.But I need to learn how to size a system alittle better.Can : you help me?Im looking for sizing of residential plumbing.Some kind of reference to help me understand sizing a little : better.GAS,COPPER&ABS!Maybe on the web?Hi, Check with the local plumbing inspector to find out what plumbing code is used in your area. Books and study booklets will be available to buy.You really need to have the book with so you can mark it with yellow highliner or underline important parts of the text.In Seattle we are using the UPC, Unifom Plumbing Code, There are two others in use in the US. Terry