[Rodney]

Welcome to the T-Shirt Forums!

but how do you know how big it is going to come if you never printed a shirt

You tell the screen printer how big you want your graphic printed and they will do the sizing for you if you have a high resolution file.

I like to use a ruler on a t-shirt to figure out how large I want a design printed.

You can also print it out on your printer and that can sometimes give you an accurate respresentation of how large it will be printed.