# 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.

Source: https://useqr.app/qr-codes-on/slide-decks · Last reviewed 2026-08-21 · UseQR is free forever, MIT licensed, no signup.

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| 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.

## Try it

- https://useqr.app/url
- https://useqr.app/size-calculator
- https://useqr.app/validate