Surface guide
QR codes on slide decks and presentations
A QR code on a projected slide is scanned from wherever the audience is sitting — often 5–10 m back. Size it as a proportion of the projected image, leave it on screen for at least 20 seconds, and never put it on a slide you advance quickly.
| Typical scan distance | 3–10 m |
|---|---|
| Minimum code width | 5–15 cm on screen |
| Error correction | M |
Size as a proportion, not in pixels
The projected width is what matters. On a 3 m-wide screen viewed from 10 m, the ten-to-one rule needs a 1 m code — impractical. In practice, aim for at least 15% of the screen height and accept that only the front half of the room will manage it.
For the back rows, a short memorable URL printed alongside does more work than the code.
Leave it up
The single most common failure is a code shown for four seconds. People need to notice it, unlock a phone, open the camera and frame it. Twenty seconds minimum, and ideally leave it on the final slide for the whole Q&A.
Contrast and background
Projectors wash out. Use pure black on pure white, never a brand colour on a photographic background. Dark rooms with bright projectors also bloom, thickening dark modules — a generous quiet zone helps.
What to link
The deck itself, the repository, the sign-up. Put it on the last slide, which is the one that stays up while you take questions — that is where the scans actually happen.