Your AI image is 1024px. The canvas is 4 feet wide. Here's the math that saved me.

I build a tool that turns text prompts into wall art you can actually hang — canvas prints, posters, 4×6 ft tapestries. The generation part is the easy part. The part nobody warns you about is this:

SDXL hands you a 1024×1024 image. A four-foot tapestry needs roughly 3,500 pixels on the long edge. A poster needs more.

For about a month I brute-forced this by upscaling everything 4× and hoping. It was slow, it blew my function memory limits, and it produced 60 MB files for products that didn't need them. Then I actually did the math, and it turned out I'd been solving the wrong problem.

Here's what I wish I'd read first.

The 300 DPI rule is for things you hold