Presentation Slides: The Back-Row Scan
Slide QR codes — for feedback forms, resource links, contact sharing, or live polls — are scanned from 3 to 10 meters by an audience holding phones at various angles, in rooms you didn't design, on projectors you didn't choose. You cannot control their distance, their angle, or their phone — so the code must be unmissably large, brutally simple, and displayed long enough to actually be scanned.
The 10:1 Rule of Thumb
At 5 m the rule suggests 500 mm on the projected image. On a typical 2 m-wide projection, that's a quarter of the image width — which is about right, and a useful gut check against the instinct to make the code "elegant" and small. As practical guidance, the code should occupy at least 10–15% of the slide's width, and never sit as a corner thumbnail. If the code is smaller than your fist at arm's length on your monitor, it's too small for the room.
Recommended Size
On screen, aim for a code at least 150 mm (6 inches) across on the projected image for rooms up to 5 m deep; scale up for larger venues — a 10 m hall needs 300 mm or more. In slide-design terms: make it the largest element on the slide. Timid codes on slides are the most common conference failure, and the fix is free.
Substrate and Printing (Digital)
There is no print substrate — but the display chain is the substrate, and it behaves like a bad print job when neglected. Projector lumens, ambient light, and screen material all degrade the code. High contrast is non-negotiable: pure black modules on a pure white panel. Brand-colored codes, transparency effects, and codes over background images all wash out under projection — save the branding for elsewhere on the slide.
Placement and Practical Tips
- Correct keystone before presenting — keystone distortion turns squares into trapezoids and punishes edge modules first. Physical projector placement beats digital correction, which resamples and softens the image.
- Leave the code static on screen for at least 10–15 seconds; nobody scans a code that animates in and vanishes with the next slide. Park it on the closing slide during Q&A.
- Test from the back row with a mid-range phone, not from the front row with a flagship — your audience's hardware is average by definition.
- Keep the URL short and the landing page instant — conference Wi-Fi is famously hostile, and a slow page wastes the scan.
- Announce the code: "scan this for the slides" converts far better than a silent symbol.
Common Mistakes
- Animating the code (flying in, fading, spinning) — motion plus distance equals failure.
- Placing the code over a busy background image instead of a clean white panel.
- Projector eco-mode dimming the image until the code's contrast collapses — run full brightness for code slides.
- Removing the slide before the back row has had time to focus, aim, and scan.