QR codes on business cards and invoices: size, contrast and testing

A QR code on a business card, an invoice or a flyer only works if a phone camera can read it on the first try. Most failures come from three things: the code is too dense for its printed size, the margin around it was cropped, or the contrast is wrong. This post, part of our sharing and presence guides, gives the size math with real numbers.

What decides how big a QR code must be

A QR code is a grid of squares called modules. According to DENSO WAVE's version table, the smallest code (version 1) is 21 × 21 modules and each version adds 4 modules per side, up to 177 × 177. The more characters you encode and the higher the error correction, the higher the version. At a fixed printed width, more modules means each module is smaller, and small modules are what phone cameras struggle with at a distance, in low light or on glossy paper.

Read the table the other way to size a code: to keep 0.8 mm modules with the long tagged URL, the code would have to be 3.6 cm wide, which doesn't fit comfortably on a 3.5 × 2 inch card next to your name. That's the practical case for short links on print.

The quiet zone: four modules of blank space

DENSO WAVE's guidance on the code area says a QR code needs a margin four modules wide on all sides. Designers often crop it to make the code fit, or place it against a patterned background, and scanners then can't find the edges. Measure the margin in modules, not millimeters: for a 0.8 mm module, 4 modules is 3.2 mm of plain background on each side.

Which error correction level to choose

Error correction lets a scanner read a damaged or partly covered code. DENSO WAVE's error correction page gives the recovery capacity of each level: about 7% for L, 15% for M, 25% for Q and 30% for H, and notes that M is the level most often selected. Higher levels make the code denser, so they cost size. Use M for cards and invoices; use Q or H only when a logo sits on top of the code or the surface is rough (fabric, kraft paper, outdoor signs).

Contrast and printing

• Dark modules on a light background. Inverted codes (light on dark) fail on some scanner apps.
• Keep strong contrast: black or a dark brand color on white or cream. Pale gray, yellow or gradients across the code reduce reads.
• Export as SVG for print so the edges stay sharp at any size; PNG is fine for screens and PDFs.
• Avoid placing the code over a fold, a spot varnish or a foil finish that reflects light.
• DENSO WAVE's module size guidance recommends each module be at least 4 printer dots, which is about 0.17 mm at 600 dpi. That's the printer's floor, not a comfortable size for phone scanning.

Static vs dynamic: put a short link behind the code

A QR code is static: the URL is printed into the pattern and can never change. If the code points straight at your portfolio page and you later move the portfolio, 500 cards stop working. Point the code at a short link instead, and change where the short link goes whenever you need to. You also get a click count for the print run, which a direct URL can't give you. For the page those codes usually lead to, see what to put in your link in bio.

Test checklist before you print

1. Print one proof at actual size on the same paper, not on screen.
2. Scan it with two different phones (one iPhone, one Android) using the built-in camera app.
3. Scan from 30 cm away and at an angle, in normal indoor light.
4. Check that the URL the phone shows is the short link you expect, and that it opens on mobile.
5. Check the margin: at least four modules of plain background on all four sides.
6. If you put the code on invoices, scan it from a printed invoice and from the PDF on another screen.

Worked example

In SoloWOS

In SoloWOS you create short links with QR codes: each short link has a QR code you can download as SVG or PNG, generated at error correction level M. The downloads already include the four-module blank margin, so don't crop it when you place the code in your layout. You can change a link's destination at any time and the printed code keeps working. Short links count clicks as daily totals with country, device and referrer, without tracking individual people. Solo ($15/month) includes 200 short links. For a one-off code without an account, use the free QR code generator.