How big should a printed QR code be?

A QR code has no natural size. The same pattern can be a centimetre wide on a business card or a metre wide on a wall, and whether it scans depends on three things: how far away the phone is, how many modules the pattern has, and whether the print has preserved the contrast the scanner needs. This article gives the rules of thumb and explains where each one comes from.

The distance rule of thumb

The widely used starting point is that a code should be about one tenth of the distance it will be scanned from. A code read from 30 centimetres — a table tent, a flyer in the hand — can be around 3 centimetres wide. A poster read from two metres wants a code around 20 centimetres. A banner across a street, scanned from ten metres, needs a code a metre across. The rule is not a law; it comes from the fact that phone cameras need each module of the code to land on a handful of sensor pixels, and the angle a module subtends shrinks in proportion to distance. It assumes a code of ordinary density. A denser code — more modules in the same square, because the encoded text is longer or the error correction is higher — needs to be larger for the same distance, because each of its modules is smaller. For a short link at the typical 25 to 33 modules across, SWAPQR's studio suggests a minimum print size of about 2 centimetres, and shows a per-design figure in the code's details; treat that as the floor for close-range scanning, not as the size to aim for.

Modules and the quiet zone

The unit that decides everything is the module: one of the small squares in the grid. A version 1 code is 21 modules across; each higher version adds four, so a short link usually lands around version 2 to 4 (25 to 33 modules) and a long address with parameters can push past version 10 (57 modules). To decide a print size, think in millimetres per module rather than centimetres per code: a common guideline is that a module should not print smaller than about 0.5 mm for close scanning, and most printers cannot hold a crisp edge much below that anyway. Multiply the module count by the module size and you have the code; then add the quiet zone. The standard requires a light margin of four modules on every side of the pattern. Scanners use that empty border to find where the code begins, and a border cut short by a tight crop, a coloured background or an adjacent line of text is one of the most common reasons an otherwise perfect code refuses to read. Export with the margin included and do not let the layout eat it.

Error correction: L, M, Q and H

Every QR code carries redundant data so that a damaged pattern can still be decoded. The standard defines four levels: L recovers up to about 7% of the codewords, M about 15%, Q about 25% and H about 30%. Higher levels are what let a code survive scratches, print wear, a fold or a logo placed over the middle. The cost is density: the extra recovery bytes take up modules, so the same link at level H may need a higher version than at level L, which means smaller modules for the same print size, which means a larger print for the same scan distance. There is no free level. M is the usual balance for a clean print with no logo. If the code will be handled, laminated, exposed to weather or overlaid with a graphic, go to Q or H and print it larger to compensate. SWAPQR raises the error correction automatically when you add a logo, because a logo covers modules and something has to pay for that; a photo code needs the highest level for the same reason, and the studio says so.

Print failures you can avoid

Most scan failures in the field have nothing to do with the encoding and everything to do with the print. Low contrast between the two colours is the first: a mid-grey on white, a dark blue on black or a pale pastel pair may look fine on a screen and be unreadable to a camera, and the studio warns when the contrast between your chosen colours is too low. Inverted colours — light modules on a dark background — read on many modern phones but fail on plenty of other scanners, so unless you have tested with the readers your audience uses, keep the modules darker than the background. Glossy laminate and metallic or reflective stock throw specular highlights that wash out whole regions of the pattern under a lamp or the sun; a matt finish is safer. Printing the code too small is the classic business-card mistake: a card is scanned from 15 to 20 centimetres, which by the distance rule wants a code of 1.5 to 2 centimetres, and a long tracked address at 1 centimetre simply will not have enough module size to survive. Trimming into the quiet zone, resizing a PNG until its edges blur, and placing the code across a fold are the rest of the list.

A checklist before you order the run

Work backwards from the scan distance to a size and check it against the module count of your particular code. Use the SVG for anything going to a print shop — it stays sharp at any size — and the 1024-pixel PNG for stickers and office printing where it will not be enlarged much. Keep the four-module quiet zone clear of text, borders and background art. Choose an error correction level that matches the abuse the print will take, and accept that a higher level means a larger print. Keep the dark colour dark and the light colour light, and prefer a matt finish. If the destination is long, consider a dynamic code: the short redirect link produces a smaller pattern, which is the single most effective way to make a code scan at a given print size. Then, before committing to the quantity, print one at the real size on the real stock and scan it with a phone from the real distance, in the real lighting. A code that reads from a monitor tells you nothing about a code on laminated card under a spotlight.