Not true heating dimensions. it says 15 x12 but since ive been using this, theres a boarder of the metal that heats up but not enough. ive messed up alot of shirts because of this, because i tried putting medium pieces to heat transfer and most of them along the edges come out faded. Although the metal for the heat press would be 15x12, i would say, because of the heat distribution, its probably around 10x8 less. do not recommend for large or medium art size shirts. I did try to do multiple presses, but because of the inconsistent heat on the edges, it's hard to tell where it's going to successfully transfer so it still came out faded... unless you plan on using it for small pieces, i wouldn't recommend.