DPI (print resolution)
DPI (dots per inch) is how many printed dots fit in an inch. Higher DPI means finer detail, and 300 DPI is the usual minimum for crisp printed QR codes.
DPI measures print resolution. At 300 DPI a printer lays down 300 dots per inch, enough to render a QR code's module edges cleanly. Print a low-resolution image too large and the modules get fuzzy, and a scanner that can't tell one module from the next gives up.
Two fixes: print at 300 DPI or higher, or use an SVG, which has no fixed resolution and is sharp at any size. For sizing the code to the scanning distance, use the size calculator.
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