Customers ask all the time, how big should the image be? What is the ideal location?
I have looked at hundreds of thousands of pieces of art going on shirts and even more shirts. I still need to see what it is going to look like. Does that mean I want to print the shirt to see? NO NO NO, a thousand times NO! Does that mean I can look at a mock up of the shirt on my phone and decide? NO!
Where size is critical and we are not sure, we print out the art at various sizes, cut it out crudely and quickly with scissors and tape it to the shirt. We then do NOT stare at it in our hands, we rather have somebody stand about six to eight feet away and evaluate how it looks. That’s real world figuring out size and location.
I often have people look at a mock up that is approximately one inch across on their phone, so the design is 3/8 of an inch and they ask to reduce the size from 6 inches to 5 inches. I’m sorry, but that is imperceptible on a phone.
A print, scissors, tape, your eyes. Maybe a ruler. That’s what you need.