# 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.

Source: https://useqr.app/docs/design/rounded-vs-square-modules · Last reviewed 2026-08-21 · UseQR is free forever, MIT licensed, no signup.

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## 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](/docs/print/qr-code-size-for-print), 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](/glossary/version) gives bigger modules, which helps every style.
- **For raster output**, respect the [300 DPI floor](/docs/print/qr-code-dpi-for-printing);
  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](/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](/docs/design/custom-eye-shapes)
(UseQR defaults `style=rounded` to rounded eyes), and it is the least risky entry in
the [module shape comparison](/docs/design/qr-code-module-shapes-compared) — 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](/validate), 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.

## Try it

- https://useqr.app/url
- https://useqr.app/validate
- https://useqr.app/size-calculator