The 10:1 QR code distance rule, derived

Print a QR code at least one tenth as wide as its scanning distance. At that ratio the code fills roughly 8% of a phone camera's frame, giving the decoder around 4 pixels per module on a mid-density code. Switch to 8:1 in poor light, at an angle, or for dense codes.

The rule

minimum printed width = scanning distance ÷ 10

A code read from 50 cm needs 5 cm; from 2 m, 20 cm; from 10 m, 1 m. The width is the code itself — the quiet zone is additional clear space, not part of the measurement.

Where the ten comes from

The rule is camera arithmetic, not folklore.

A phone's main camera has a horizontal field of view of roughly 65–70°, which means the frame spans about 1.2–1.4 × the distance to the subject. A code sized at distance ÷ 10 therefore occupies roughly 7–8% of the frame width.

Detection does not run on the full 12-megapixel sensor. Scanners typically process a preview stream of 1080–1920 pixels across, so that 7–8% slice of frame is 90–160 pixels across the code. Spread those pixels over a version 4 symbol — 33 modules per side — and each module gets about 3–5 pixels.

A decoder needs roughly 2–3 pixels per module to threshold dark from light reliably. So ten-to-one lands a mid-density code just above the sampling floor, with margin left for imperfect focus, hand shake and lighting. That is the whole derivation: field of view, preview resolution, pixels per module.

The table, at 10:1 and 8:1

Scanning distance	10:1 width	8:1 width
30 cm	3 cm	3.8 cm
50 cm	5 cm	6.3 cm
1 m	10 cm	12.5 cm
2 m	20 cm	25 cm
3 m	30 cm	37.5 cm
5 m	50 cm	62.5 cm

When to use 8:1

Moving to 8:1 buys 25% more pixels per module. Spend that margin whenever the derivation's assumptions fail:

Low light. Sensor noise eats the contrast the thresholder relies on — common for outdoor and evening placements.
Steep angles. Beyond about 30° off axis, modules foreshorten in one dimension.
Dense codes. Version 6 and above spread the same pixels over more modules.
Glare-prone surfaces — laminated menus, glass, gloss posters.
Older or budget phones with lower preview resolution.

What the rule assumes

It assumes a moderate payload, roughly version 2–4. A 40-character URL at error correction M qualifies; a vCard does not. For dense payloads the per-module maths takes over, which is exactly what the size calculator computes — it returns a larger answer than 10:1 whenever density demands it, as explained in how the calculator works.

The rule also says nothing about print quality. Each module still has to clear the substrate's floor — 0.4 mm for coated offset, 0.5 mm for thermal at 203 dpi — covered in the size pillar. And no ratio rescues artwork that does not decode in the first place, so run it through the validator before committing to print.

FAQ

What is the 10:1 rule for QR codes?

Printed code width should be at least one tenth of the scanning distance. A code scanned from 1 m should be at least 10 cm wide. It is a sizing floor derived from phone camera field of view and the decoder's need for a few pixels per module.

How far away can you scan a QR code?

About ten times its width in good conditions: a 10 cm code from roughly 1 m, a 1 m code from roughly 10 m. Poor light, steep angles and dense payloads shorten that range, which is why conservative designs use eight times the width.

When should I use 8:1 instead of 10:1?

In dim light, on glossy or glass surfaces, when readers approach at an angle, when the code is version 6 or denser, or when your audience skews toward older phones. The extra size buys 25% more pixels per module.

Does the quiet zone count toward the 10:1 width?

No. The ratio applies to the code pattern itself. The four-module quiet zone is required clear space on top of that width, on every side.