I cant take the back off to measure the ground glass. Although I now firmly believe its a 3.25x4.25, and I'm kinda having buyers remorse over it. I think I was smitten by the thought of that big ole negative, but honestly... how much would I actually shoot it. The Hasselblad barely gets enough exercise as it is.
You can measure the ground glass from the side you can see. I can see it in the photo. Just use a tape measure. The difference between 3.25x4.25 and 4x5 is easy to see and measure. Precision is not required.