Design
Rounded vs square QR modules — when rounding costs you
Rounded modules are safe because decoders sample near module centres, which rounding never touches — a 0.32-module corner radius still keeps about 91% of the ink. Rounding only becomes a risk in tiny print, where the radius shrinks to a pixel or two and blur erodes the thinned corners of every module.
Why rounding is safe
A decoder locates the grid and samples each cell around its centre. Rounding a module's
corners removes ink only from the four corners — the region a sampler cares about least.
UseQR's style=rounded uses a corner radius of 0.32 × the module size, which
removes about 9% of the ink: each corner loses r²·(1 − π/4) of area, and four
corners at r = 0.32 comes to roughly 0.088 of the cell. The centre remains solid, the
cell remains 91% dark, and to a decoder the module is simply dark.
This is the honest general answer: at normal sizes, rounded and square modules scan indistinguishably. Choose between them on looks.
Where rounding starts to cost
The corner radius is a fixed fraction of the module, so as the module shrinks, the radius shrinks faster than the eye notices:
| Printed code width | Version 5 (45 cells incl. quiet zone) | Module size | Corner radius at 300 DPI |
|---|---|---|---|
| 5 cm | 45 cells | 1.11 mm | ~4.2 px |
| 3 cm | 45 cells | 0.67 mm | ~2.5 px |
| 2 cm | 45 cells | 0.44 mm | ~1.7 px |
At the 2 × 2 cm print floor, a version 5 module is 0.44 mm — about 5.2 px at 300 DPI — and the rounding is under 2 px. At that scale two things happen at once: the printer can no longer render the curve cleanly, and ink spread plus optical blur eat disproportionately into the already-thinned corners. Each module drifts from 91% ink toward something less, and the code's margin erodes across every module simultaneously rather than in one visible place.
The practical rules that fall out:
- At 3 cm and above (close-range print), rounded is a free choice.
- At or near 2 cm, prefer square — or shorten the payload so a lower version gives bigger modules, which helps every style.
- For raster output, respect the 300 DPI floor; below it the corners blur regardless of size. SVG export sidesteps resolution loss entirely.
- For distance scanning, size with the 10:1 rule via the size calculator first; a correctly sized code has module sizes where rounding is irrelevant.
Rounded modules, square judgement
Rounding pairs naturally with rounded eye styles
(UseQR defaults style=rounded to rounded eyes), and it is the least risky entry in
the module shape comparison — meaningfully
safer than dots, which carry only ~55% ink. As always the proof is a decode of the
final export at final size: run it through the validator, and for small
print, decode a photograph of a printed proof rather than the screen preview.
FAQ
Do rounded QR codes scan as well as square ones?
At normal sizes, yes — decoders sample module centres, and rounding only removes corner ink, leaving about 91% of each module. The difference only matters in very small print, where the corner radius drops below what the printer and camera can resolve.
When should I use square modules instead of rounded?
At small print sizes — around the 2 × 2 cm floor — and whenever the code is dense or will be scanned in poor conditions. Square modules carry the maximum ink per cell, which is exactly the margin small print consumes.
How round is too round?
A radius around a third of the module, like UseQR's 0.32, is conservative. As the radius approaches half the module the shape becomes a dot, ink coverage falls toward 55%, and the risks of dot-style codes apply instead.
Does rounding affect the corner squares too?
Only if you choose a rounded eye style — module style and eye style are set independently. The three finder squares tolerate rounding well, provided their 1:1:3:1:1 proportions and dark ink remain intact.
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Related
- QR code design best practices — seven rules ranked — The seven design rules that decide whether a styled QR code scans, ranked by how often breaking them kills codes, with the number behind each rule.
- QR code module shapes compared — square to organic — Square, rounded, dot, diamond, star, bar and organic QR modules compared by ink coverage and scan risk, with the geometry numbers behind each style.
- Dot-style QR codes — how far circles can go — Dot modules are circles at 84% of the cell width, about 55% of the ink. Why that works, the density limit where it breaks, and why the eyes stay solid.
- QR code frames and CTA labels, done safely — Frames and scan-me labels help when they name the destination and sit outside the quiet zone. Placement rules, sizes, and the label parameter in UseQR.