Every print-on-demand platform hands new authors the same thing: a flat PNG "template," a scattering of red and blue guide boxes, and a page of instructions telling you to build your wraparound cover around it yourself, in whatever design software you happen to own. Change your page count by twelve pages after the fact — which happens to almost everyone, usually after a proofreader gets involved — and the spine width shifts, and you're rebuilding the whole wrap from scratch.
I lost more afternoons to this than I'm comfortable admitting across eighteen books. Not because the maths is hard — spine width from page count and paper stock is a known formula — but because doing it by hand, checking it, getting the barcode zone right, and re-checking it every time something changed was exactly the kind of repetitive, error-prone task that has no business still being manual in 2026.
So Spinework exists now. Pick a trim size — the standard presets or your own custom dimensions — enter your page count and paper stock, and it calculates the exact spine width and builds the full back-spine-front wrap around it, live, as you type. The barcode zone is kept clear by construction, sized to the standard ISBN barcode. Bleed and safety guides follow the industry-standard red/blue convention, with a proof export for checking your work and a clean file for actually sending to print.
The detail I'm most pleased with: the moment you set your trim size, Spinework shows you the exact source-image dimensions your cover art needs to be. No more designing at a guess and hoping nothing gets cropped or letterboxed at the edges.
It's free, it runs entirely in your browser as a single file, and nothing you upload ever leaves your machine — no server, no account, no progress bar to watch. Download it once and it keeps working offline, forever. Get Spinework here — it lives alongside The Bindery as the second tool I've built because the thing I actually needed didn't exist yet.