QR codes on curved surfaces

Curvature foreshortens the far edges of a code and decoders only tolerate so much of that distortion. Keep the code width to one sixth of the cylinder circumference or less, centre it on the visible face, and for narrow tubes move the code to a flat surface such as the cap or a tag.

What curvature does to the symbol

Wrap a flat square around a cylinder and the camera no longer sees a square. Modules at the centre of the code face the lens; modules near the left and right edges tilt away, foreshortening horizontally until, at 90° around the curve, they vanish entirely. The decoder receives a symbol whose module width shrinks progressively toward two edges — a distortion that is neither a clean rotation nor a clean perspective skew.

Decoders have real tolerance here. The three finder patterns let the software fit a perspective transform, and from version 2 upward alignment patterns provide interior anchor points that correct smooth local warping. That machinery is why bottle labels work at all. But the correction models assume mild, continuous distortion — it runs out well before the geometry does.

The one-sixth rule

A practical, testable limit:

maximum code width ≈ cylinder circumference ÷ 6

At one sixth of the circumference the code spans 60° of arc, and the outermost modules are tilted about 30° from the camera — roughly the same tolerance decoders show for scanning at an angle on flat surfaces. Beyond that, edge modules compress faster than error correction can compensate.

Worked examples with real diameters are on the cylindrical packaging page — a slim 330 ml can, for instance, has a circumference of about 16.6 cm, capping the code at roughly 2.8 cm.

Remember the cap interacts with the ten-to-one distance rule: a 2.8 cm code is only good to about 28 cm of scanning distance, which is fine for an item held in the hand and useless on a shelf across an aisle.

Orientation: only one dimension needs to curve

A QR code is square, so one of its dimensions must wrap around the circumference — but only one. Keep the other aligned with the cylinder's long axis, where the surface is flat. Practically:

Apply labels so the code sits level, centred on the natural viewing face, away from label seams and edges where the wrap tightens visually.
On tall narrow items — wine bottles, tubes, pens — the flat direction runs vertically. A QR code scans at any rotation, so there is no penalty for placement that favours the axis.
Concave curves (inside a wristband, a scooped surface) behave like convex ones optically, with the added problem of self-shadowing. The same one-sixth budget applies.

When the cylinder is too thin

Below roughly a 3 cm diameter (circumference under ~9.4 cm), the one-sixth rule caps the code at ~1.6 cm, and dense payloads stop fitting at scannable module sizes. Honest options, in order:

Move the code to a flat surface — the cap, the base, a hang tag, or the carton the tube ships in.
Shorten the payload so a lower version keeps modules large — see why longer URLs make denser codes and check the result in the size calculator.
Rectangular rMQR can run its long axis along the cylinder, but rMQR support in stock phone cameras is far from universal — do not use it for consumer-facing codes yet.

Always test on the object

Print a proof, wrap it on the actual item — not a larger stand-in — and scan with several phones at the realistic distance. Shrink-sleeve and flexo processes add their own distortions on top of geometry, covered under cylindrical packaging.

FAQ

Can a QR code work on a curved surface?

Yes, within limits. Finder and alignment patterns let decoders correct smooth distortion, so codes on bottles and cans scan reliably when the code width stays at or under one sixth of the cylinder's circumference.

How much curve can a QR code handle?

About 60° of arc — a code spanning one sixth of the circumference. At that width the outermost modules tilt roughly 30° from the camera, which is within normal decoder tolerance. Wider than that, edge modules compress beyond recovery.

Why does my bottle QR code not scan?

Usually the code is too wide for the diameter, so edge modules foreshorten too far. Measure the circumference, divide by six, and compare with your code width. Glare from glossy labels on curved surfaces is the other common culprit.

Where should a QR code go on a tube or bottle?

Centred on the main viewing face, level with the axis, away from seams. If the diameter is under about 3 cm, put the code on the cap, the base or a tag instead of the curved wall.