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Go / No-Go Tool

QR Minimum Size Checker

Check whether a planned QR size is safe for its scan distance, device class, and lighting — with the required size and the margin you have.

1. Your plan

Formula and assumptions

Required width = scan distance ÷ ratio, with the ratio set by conditions: 10:1 for good light on an average or better phone, 9:1 when the audience includes older or budget phones, and 8:1 for dim light or glare. These ratios are stated planning rules built on the standard 10:1 optical rule of thumb. The check compares your planned width against the required width and reports the margin; a positive margin means the plan passes with room to spare.

Verdict
✕ Too small
Required: 100.0 mm · Planned: 40 mm · Margin: -60%
Ratio applied10:1 distance-to-size
Scan distance1 m
Conditionsaverage, good lighting

Enlarge the code to at least 100 mm, shorten the payload so the modules grow, or move the code closer to where people stand.

At the required size, a version-5 code (37 modules) has modules of about 2.70 mm.

A Go / No-Go Check Before You Print

Most QR failures are decided before the file ever reaches the printer, in the moment someone chooses a size that looks right on screen. On a laptop, a 25 mm code looks generous. On a poster viewed from three metres away, the same code is a speck. The checker on this page turns that judgement into arithmetic: given the distance people will actually scan from, the phones they will use, and the light they will stand in, it tells you the minimum width that stands a chance, and whether your planned size clears it. It is a go / no-go gate, and it belongs before artwork approval, not after.

Distance is the dominant factor

The rule is the standard 10:1 distance-to-size ratio: the code should be at least a tenth as wide as the distance from which it will be scanned. A code on a table tent scanned from 40 cm needs 40 mm. A code on a window scanned from 3 metres needs 300 mm. The ratio tightens when conditions worsen — 9:1 when the audience includes older or budget phones with weaker cameras, and 8:1 in dim light or glare. Those adjustments are planning rules, not laboratory measurements, and they exist because the real world is rarely the best case. The most common sizing error is measuring the distance from the nearest kerb instead of from where people actually stand, so measure the real viewing position.

What to do when the plan fails

A failing check leaves three honest options. Enlarge the code, which is the right answer whenever space allows. Shorten the payload, which drops the version and enlarges every module without changing the print size — a short redirect is the classic fix. Or move the code closer to the viewer: a code on the door at eye level beats a code high on the window, even if the window version looks more impressive. What is not an option is hoping customers will walk closer. Some will, most will not, and the ones who do not are the campaign's lost conversions. A code that fails the check should not be printed on the assumption that behaviour will save it.

The check that still matters after the maths

  • Print a proof at final size on the real substrate and scan it from the real distance.
  • Test on an older phone, not just the newest one in the office.
  • Test in the actual light: daylight, dusk, and artificial light if the code lives outdoors.
  • Check the quiet zone survived the layout — a cropped margin fails codes that the maths approved.
  • Re-check after any change to payload, placement, or substrate.

The maths takes ten seconds. The proof takes ten minutes. Both are cheaper than a reprint.

Frequently Asked Questions

What is the 10:1 rule for QR codes?

The code width should be at least one tenth of the scanning distance: 1 metre of distance needs a 100 mm code. It is the standard optical rule of thumb, tightened to 9:1 for older phones and 8:1 for dim light or glare in this checker.

My code passes the size check but still fails — why?

Size is necessary, not sufficient. Contrast, a cropped quiet zone, a dense payload, glare, or a damaged print can each fail a correctly sized code. Check contrast, margin, and a printed proof as well.

Should I design for flagship phones or budget phones?

Budget phones. Your audience carries a mix, and a code that only works on a flagship silently excludes a large share of scanners. The checker applies a stricter ratio when older or budget phones are expected.

Does moving the code closer really help?

Yes — distance is the dominant factor. A code at eye level on the door, scanned from under a metre, can be far smaller than the same code placed high on a window and scanned from three metres away.