Skip to main content
Two numbers belong on every print spec you hand a shop: a quiet zone of at least 4 modules on all four sides, and a printed size of at least about 20–25 mm (roughly 1 inch) square. Both are about whether a phone camera can decode the code at all — and both fail silently, producing a piece that looks perfect and does not scan.

​
The quiet zone: 4 modules, and nothing may cross it

A module is one of the small squares the code is built from. The quiet zone is blank space on all four sides, at least 4 modules wide, and the scanner uses it to find the code’s edges. Nothing can cross into it. Not a logo, not a border, not a line of text, not a mounting hole, not the edge of a laminate or an overlay film. Any of those can stop the code decoding while leaving artwork that looks entirely correct to the eye. Mark the quiet zone on your spec as a boundary, not an afterthought — the shop needs to know where the clear space ends, not only where the code sits. This matters most on small tags, where a fixing hole and the code are competing for the same few millimeters.

​
The exported PNG has a 2-module margin, not 4

Worth knowing if you are laying codes out yourself: the PNG QRtub exports carries a white margin two modules wide around the code, not four. Print specs commonly ask for four. So do not treat the image’s built-in border as the quiet zone — add clear space around the placed image in your layout, or hand the shop a spec that tells them to.

​
Minimum size: about 20–25 mm

As a rule of thumb, do not print a code smaller than about 20–25 mm square if it needs to be reliably scanned by a phone camera. Below that, the modules get small enough that camera focus, print resolution, and material texture start to matter more than the code itself. Scanning distance pushes that number up, not down. A code on a plant room door read from two meters away needs to be much larger than one on a handheld tool.

​
The PNG scaling constraint

QRtub exports QR codes as PNG only: 1024 × 1024 pixels, black on white. There is no vector option, no control over size or colors, and no exposed error-correction setting — QRtub uses the generator’s default and does not surface the level. That has two practical consequences. Do not scale a PNG much past 1024 pixels of print area. At 300 dpi, 1024 pixels is roughly 87 mm — comfortable for a tag or a sticker, tight for a plaque, and not enough for a sign. Enlarged well beyond that, the code’s edges soften enough to stop scanning. You cannot compensate for damage with error correction. For a piece that will live outdoors, be laminated, or get scratched, there is no level to raise. Compensate with size instead: print the code larger than you otherwise would, and print its address in readable text nearby so someone can type it when the code is damaged.

​
When you need it bigger than a PNG allows

Do not go looking for a vector export — QRtub does not have one. Give the shop the Full URL column from your exported print list and let them generate each code themselves at the exact size their press needs. That is normal practice rather than a workaround. The URL is everything a QR generator needs, and it puts the format and rendering choices with the people who know the press.