KDP's cover requirements read like a spec sheet and each line catches a different mistake. Dimensions: ideal 2560 x 1600 px, minimum 1000 x 625 px, nothing above 10,000 px on either side. Ratio: at least 1.6:1 height to width, so a square export from a design tool will not fit the slot. File size: under 50 MB. Colour: RGB, saved without colour separation, because that is a print-prep option and KDP is a screen-first store. Resolution: KDP lists 72 dpi as the display value but asks for a source at a minimum of 300 PPI and tells you to avoid over-compressing because it degrades how the cover renders on reading devices. The practical order of operations is therefore resize first, then compress: get the canvas to 1600 x 2560, confirm the ratio, then pull the file under 50 MB only if it is over. A cover that already fits does not need re-encoding at all — and KDP re-compresses it for the site regardless. Skwish resizes to exact dimensions and compresses in the same pass, in the browser, with the before and after shown.