QR code size for a shop window

Pavement distances

Position	Distance	Minimum code width
Eye-level decal, walked up to	50 cm	5 cm
Window-shopping distance	1 m	10 cm
Across the pavement	2 m	20 cm

The middle row is the design case: people browsing a window stand about a metre back. 10 cm at eye level (1.4–1.6 m) is the standard shop-window answer, scaled up to 20 cm if the pavement is wide and you want scans from strollers-past. The general distance arithmetic is the ten-to-one rule; glass then takes its own cut.

Glass takes a cut

A window is a semi-mirror. Whatever is behind the reader (the bright street) reflects off the glass and overlays the code, and the scan succeeds only where the code's contrast beats the reflection. Three practical consequences:

1. Put the code on the glass, not behind it. A poster on a stand 30 cm inside the window adds a second reflective pass and an air gap that doubles ghosting. A vinyl decal applied to the inside surface of the glass reads dramatically better. The material options are covered in QR codes on glass.
2. White backing is non-negotiable. Dark modules printed on clear film float over whatever the shop interior happens to be (shelving, lighting, movement), so the background luminance is uncontrolled and the contrast rule fails intermittently. Print the code with an opaque white layer behind it.
3. Leave angle margin. Readers instinctively shift sideways to dodge their own reflection, scanning from 20–30° off axis; the size table above already assumes some of that, but it is one more reason not to print at the bare minimum. The geometry is the same as any glossy surface.

The after-hours failure

The failure unique to windows: the phone torch. After dark, an unlit window makes the phone switch its torch on, and glass returns that beam straight into the lens as a brilliant hotspot, usually dead-centre on the code the user is aiming at. If after-hours scanning matters (estate agents' windows, "we're closed, order online" signs), keep the window display lit, or place the code where ambient street light falls on it. A matt decal also scatters the torch beam instead of mirroring it.

EC M is sufficient, window decals live indoors-facing-out and take little physical damage; glare and reflection are contrast problems that error correction cannot repair anyway. Check the size against your real pavement with the size calculator, verify the artwork, and test the finished window at night as well as noon. Display ideas for the rest of the window are on the shop windows surface page.

FAQ

How big should a QR code be in a shop window?

10 cm for people browsing at about a metre, 20 cm to catch passers-by across the pavement, 5 cm only for eye-level decals people approach closely. Mount it at 1.4–1.6 m so it sits at adult eye height.

Why is the QR code in my window hard to scan?

Reflection. Glass overlays the street scene on the code, and a poster behind the glass adds a second reflection and ghosting. Use a white-backed decal on the glass itself, and check it at night, when phone torches bounce straight back.

Can I print a window QR code on clear vinyl?

Print the modules over an opaque white backing layer. On fully clear film the code's background is whatever is inside the shop, so contrast varies minute to minute and scans become unreliable.

Does a shop window QR code work at night?

Only if light falls on it. An unlit window triggers the phone's torch, which reflects off the glass into the camera as a hotspot. Keep the display lit after hours or position the code under street lighting.