How big the QR code on your slide must be
A code in the corner of a slide is scanned by the front rows only. Give the link, the screen and how far back the last row sits, and see how much of the slide's height the code needs, which rows can read it, and a 1920 × 1080 slide to drop into your deck. It all runs in your browser.
In metres. The image is 1.7 m high.Hotel and meeting-room screens are often 2.5-3 m (8-10 ft) wide; a big hall's can be 6 m or more.
Rows on 36-inch (0.91 m) centres, the usual conference spacing. Row 20 sits 20.4 m from the screen.
What the back row needs
For row 20 (20.4 m), the code needs 63% of the slide height to read reliably (3 camera pixels a square), and 42% at the bare minimum (2 pixels). With its white margin it can take at most 76%.
It fits. Make the code the slide's main thing, centred, with the short address under it.
Try 12% to see what a corner code reaches. On a 16:9 PowerPoint slide (13.33 × 7.5 in) 65% is a code 4.9 in tall.
| Row | From the screen | Camera px a square | Verdict |
|---|---|---|---|
| 1 | 3.0 m | 21.1 | reads |
| 5 | 6.7 m | 9.5 | reads |
| 10 | 11.2 m | 5.6 | reads |
| 15 | 15.8 m | 4.0 | reads |
| 20 | 20.4 m | 3.1 | reads |
At 65%, everyone up to row 20 reads it without zooming. A phone's main camera in a 1,920-pixel frame sees 1,445pixels per metre of screen at 1 m. Google's barcode scanner needs 2 pixels a square; 3 reads reliably, and a washed-out projector image needs the margin.
The slide appears here.
Before the talk
- Stand at the back and scan it on the real screen, with the room lights as they'll be.
- Leave it up for 30 seconds and through the questions: people need about 12 seconds once the phone is out.
- Say “zoom in if you're at the back”. Pinching to 2× halves the size the code needs.
- Use a short link you can repoint, so the code in the recording still works when the slides move.
Where the numbers come from, what the code should open and how to compare events with one link each: a QR code on the last slide of a talk. Need the short link first? Make one with its QR code, or one per event in one go. Printing on paper instead? The print size calculator works by reading distance.