QR Code Generator for Labels

Sizing QR codes for print

Print resolution and DPI

A label printer set below 203 DPI renders each module as roughly 1.5-2 pixels, and rounding at that resolution warps square modules into rough rectangles. Thermal label printers (203 or 300 DPI) need at least 8 dots per module to keep edges clean; at 203 DPI that puts a practical floor around 0.32 mm per module before dot gain distorts the pattern further. Inkjet and laser office printers behave differently: toner and ink both spread 0.05-0.15 mm past the vector edge on uncoated stock, which is why a module spec'd at exactly 0.4 mm can still fail on cheap paper even though it meets the 1:10 sizing rule. Export at the highest resolution the generator allows (vector SVG if printing from a design tool, otherwise 300+ DPI PNG) and let the printer downsample, not the reverse.

Error correction level vs. data length

Error correction and payload length trade off directly because both consume the same fixed grid of modules. A Version 5 QR code (37x37 modules) holds about 106 alphanumeric characters at level L but only around 48 at level H, since H reserves roughly 30% of the code's data capacity for redundancy instead of payload. For labels that will get scratched, wrapped around a curved bottle, or partially covered by tape, level H is worth the capacity cost. For a static, protected label printed indoors, level M is usually enough and buys back capacity, letting you fit a longer URL without bumping to a bigger, denser version. Shortening the encoded URL (a redirect or short slug instead of a long tracking link) is the more reliable way to keep the module count low, since it lets you keep high error correction without forcing a larger physical code.

Contrast and finish on the label stock

Scanners need roughly 4.5:1 luminance contrast between the dark modules and the background to lock on reliably in mixed lighting; pure black on white gives about 21:1, so there's a lot of room before contrast becomes the bottleneck, but pairing a mid-tone brand color with white (say, a medium blue at 3:1) can sit right at the edge of failure under fluorescent glare. Glossy laminate over a label makes this worse indirectly: it doesn't change contrast, but specular reflection from overhead lighting can blank out a section of the code entirely when photographed at an angle. Matte or satin laminate scatters that reflection and scans more consistently under variable lighting. Never invert the code (light modules on a dark background) unless the specific scanner app is confirmed to support it; most default camera-based readers still expect dark-on-light and will silently fail on an inverted symbol.

Curved and small-diameter surfaces

Wrapping a QR code around a cylinder distorts the modules on the curved edges into trapezoids, and most scanners tolerate that up to a bend where the code's width is no more than about 30-40% of the surface's circumference. Past that, the outer columns of modules stretch enough that the finder patterns in the corners lose their exact 1:1:3:1:1 ratio and detection drops off fast. For jars, tubes, or bottles under about 4 cm in diameter, keep the code on a flat cap or a flat panel of the label rather than the curved body, and lean on level H error correction as a buffer against the unavoidable geometric distortion at the wrap seam.