You printed a QR code on a business card, handed it out at a networking event, and watched someone hold their phone two inches from it like they were trying to read the fine print on a prescription bottle. It worked, barely. But you're now wondering if there's an actual rule for how big these things need to be, or if everyone is just guessing.
Most people are just guessing.
The 10:1 rule
There's a ratio that works well enough for almost every situation: your scan distance divided by 10 gives you the minimum size your QR code should be. If someone will scan from 10 feet away, your code needs to be at least 1 foot across. If they're scanning from 3 feet, you need roughly 3.5 inches.
That's it. That's the rule. It's not physics-precise, but it accounts for the reality that phone cameras vary, lighting isn't always great, and people don't hold their phones perfectly still. Giving yourself a little margin above the minimum is always smart.
The ratio also assumes a reasonably simple QR code. The more data you pack into a code (a long URL, for instance), the denser the pattern gets, and denser patterns need to be larger to scan reliably. This is one reason dynamic QR codes are worth using: the encoded URL is short and fixed, which keeps the pattern simple regardless of where you're sending people. You can read more about how that works on our dynamic QR codes page.
Common sizes, from business cards to billboards
Let me just run through the contexts where this comes up most, because abstract ratios are only useful if you can picture them.
Business cards. People scan these from maybe 6 to 8 inches away. A code around 0.75 inches square works, but I'd push for a full inch if your card layout allows it. Anything smaller and you're relying on perfect lighting and a steady hand, which is optimistic for a loud conference hall.
Table tents and menus. Scan distance is usually around 12 to 18 inches. You want your code to be at least 1.5 inches, ideally closer to 2 inches. Restaurants that shrink the code to make room for more text are trading scanability for information nobody reads anyway.
Flyers and letter-sized printouts. Someone walking by a bulletin board scans from maybe 2 to 3 feet. An inch and a half can technically work at the closer end of that range, but 2 to 3 inches gives you breathing room. If the flyer is going behind glass or plastic (community boards, store windows), go bigger. Glare kills scans faster than small size does.
Posters. Think 4 to 8 feet of scan distance. Your code should be at least 5 to 6 inches across. I see a lot of event posters where the QR code is tucked into the bottom corner at maybe 2 inches. That's decorative, not functional.
Banners and billboards. This is where people underestimate most dramatically. If your banner is across a trade show booth and people are scanning from 10 to 15 feet, you need a code that's well over a foot across. For roadside billboards (which, honestly, I'm not sure work well for QR codes no matter the size, since drivers shouldn't be scanning anything), you'd need several feet. The 10:1 rule still applies, it just produces numbers that surprise people.
Quiet zone matters more than you think
The QR code itself isn't the only thing that needs space. That blank border around the code, sometimes called the quiet zone, is how the camera distinguishes "this is a code" from "this is part of the design." Most QR generators include it automatically, but designers love to crop it down or layer it against a busy background.
If your code looks fine at the right size but still scans inconsistently, check the quiet zone first. A good rule of thumb is to keep a margin of blank space around the code equal to about four of those tiny square modules in the pattern. You don't need to measure this precisely. Just don't let text, images, or borders crowd right up against it.
Test it before you print it
This sounds painfully obvious, and yet. Print a test copy at the actual size, tape it where it's going, and scan it from where people will be standing. Try it with two or three different phones if you can. The five minutes this takes will save you from discovering the problem after you've printed 500 flyers or laminated 30 table tents.
One thing that catches people off guard: a code that scans fine on screen might not scan from print. Screens are backlit and high contrast. Print introduces ink bleed, matte finishes, and ambient lighting. Always test from the physical version.
If you're building QR codes for anything that'll get printed in the real world, DSQR's free plan lets you create up to 5 dynamic codes with full customization. Worth trying before you commit to a print run.