There are so many times I see people posting that their vectors are getting rejected or are too big for certain products. The solution could be easier than you might think.
99.9% of the designs I make for my Spreadshirt shop are designed on a starting area of 9inch x 9inch in Adobe Illustrator. After much trial and error, Temple from Spreadshirt helped me come up with the 9×9 rule and it hasn’t let me down yet. Will this work for everyone? Probably.
Now I only sell t-shirts for the most part so for those other smaller products such as scarfs, hats, bibs and etc it’s not going to work. So if you’re having problems designing vectors for most of the t-shirt products at Spreadshirt I recommend you give this a try. Once I have my design ready to go, I stretch it so that it touches the right and left of my 9×9 grid. In some cases the design may be taller and therefore I stretch it flush with the top and bottom.