How big a QR code needs to be in print.

Start from the scanning distance.

The right size for a printed QR code depends on how far away the phone will be, not on how much space you have. A widely used rule of thumb is to make the code's width about one tenth of the scanning distance. At 20 cm that gives 2 cm. At 2.5 m it gives 25 cm.

It is a rule of thumb, not a requirement of the standard, and the reason is optical. Each square in the code, called a module, has to cover several pixels of the phone's camera image to be read cleanly. A camera has a fixed number of pixels, so when the distance doubles, each module covers half as many. To keep the same pixels per module, double the width of the code. A tenth is a comfortable margin for a code of about 33 modules a side, read by a recent phone in decent light.

Three things move the number. A code with more modules needs more width. Poor light, glare or an older camera need extra margin. Someone scanning while walking past needs more again. Round up, and treat the result as a minimum.

Sizes by use, with the arithmetic.

Check the sums against the space you have. A 15 cm code on an A4 page, which is 21 cm wide, leaves 3 cm each side, more than the code needs for clear space. A 25 cm code on a roll-up that is 85 cm wide takes under a third of the width. Put it between 100 and 140 cm from the floor, where hands and eyes are, because nobody crouches to scan.

Fewer modules make bigger modules.

A QR code is a square grid. The smallest, version 1, is 21 modules a side. Each version adds 4, up to 177 for version 40. The longer the address you encode, the higher the version, and at a fixed printed width every module gets smaller.

To match the 0.61 mm modules of the shortest address, the longest needs a code 3.5 cm wide, which is 57 divided by 33, or 1.7 times as wide. On a namecard that is most of the height of a 55 mm card.

The fix is to encode a short address and let it redirect. A short link such as yourcompany.com/ice27 points to the long address with all its tracking parameters, so the code stays small and sparse, and you can change the destination after the code is printed. Short link best practices covers how to choose keys.

Leave 4 modules of quiet zone.

The quiet zone is the empty margin around the code. The ISO/IEC 18004 standard for QR Code sets it at 4 modules on every side, and Denso Wave, the company that invented the code, gives the same figure. The smaller Micro QR code needs only 2, which is where the 2 module figure you may have seen comes from.

A code with a 2 module margin often still scans, because phone software is good at finding codes. It is still a risk. A dark card edge, a photograph or a line of text within a module or two of the code can make the scan fail on a bad day, and you will not know which day until you are at the show.

The arithmetic is short. For a code of about 37 modules, 4 modules is 4 divided by 37, about a tenth of the code's width. So leave a tenth of the code's width clear on every side. A 2 cm code needs about 2 mm. A 25 cm code needs about 2.7 cm. Keep text, borders, frames and image edges out of that space.

Choose an error correction level on purpose.

Every QR code carries extra data that lets a scanner repair damage. There are four levels, and Denso Wave gives the share of the code each can restore as approximate.

Higher levels cost modules. For https://yourcompany.com/ice27 the code is 25 modules a side at level L, 29 at M and Q, and 33 at H. Use level H when the code will be handled, scuffed or styled. Level M is enough for a clean print of a short address. Correction is not permission to deface the code: styling uses the same margin that a smudge would.

Contrast, glare and curved surfaces.

Send the printer a vector file.

An SVG file is made of shapes, so it stays sharp at any size. A PNG is a grid of pixels and stays sharp only up to a size. At 300 dpi, a 1024 px PNG covers 1024 divided by 300, or 3.4 inches, which is 8.7 cm. That is plenty for a namecard, a badge or a leaflet. A 25 cm banner code needs 25 divided by 2.54 times 300, about 2,950 px, so send the SVG instead.

Never save the code as a JPEG, which smears the edges, and never stretch it unevenly: modules must stay square. Keep the file's margin when you place it in a layout.

Test before you print.

Print a proof at actual size on the real stock. A screen preview tells you nothing about ink spread or glare. Then run this list, and keep the result with the artwork.

1. 01
   Step 1.

   Scan with two phones: one iPhone and one Android, at least one of them three years old or more.

2. 02
   Step 2.

   Use the built-in camera app, not a scanner app you installed.

3. 03
   Step 3.

   Scan from the target distance, from 1.5 times that distance and from 30 degrees off to the side.

4. 04
   Step 4.

   Test in the worst light you expect: hall spotlights, a dim corner, daylight with glare.

5. 05
   Step 5.

   Open the result on mobile data, not only on Wi-Fi, and check the page loads in a few seconds.

6. 06
   Step 6.

   Hold the proof against the real surface and check that nothing sits inside the quiet zone.

7. 07
   Step 7.

   Ask someone who has never seen the code to scan it without help.

8. 08
   Step 8.

   Fix what failed, then print the proof again. Only then approve the run.

For what to put on a pre-show list beyond the codes, see the trade show checklist for exhibitors. To give each piece its own address, read QR codes on collateral for source attribution.