Custom QR Stamp Generator

Every QR code carries spare copies of its own contents. Denso Wave, who invented the symbology, publishes four levels of it: L rebuilds 7 percent of the code, M 15 percent, Q 25 percent and H 30 percent. That is the number every article about putting a logo in a QR code quotes, and it is the number that gets people into trouble, because it counts codewords rather than surface area, and because of what a plate over the middle actually does to a symbol. A QR code interleaves its codewords across the whole matrix, on purpose, so that one blot cannot destroy any single block outright. The side effect is that a plate puts a little damage into a great many blocks at once, and correction is applied per block. A little everywhere is harder to survive than a lot in one place.

So we measured it instead. Every custom QR stamp in the table below was rendered to a bitmap and handed to a decoder, with the plate grown one step at a time until the decoder gave up. The payload is this page's own URL, the frame is the round one, and the render is perfectly clean, with no ink anywhere in it.

Read the L row twice. It gave out at 4.3 percent coverage against a published capacity of 7 percent, so the headline number was worth about three fifths of itself once the damage was concentrated in one square. M behaved the same way, failing at 11.1 percent against 15. Q and H were not broken by anything this builder is willing to draw, which is why the slider stops where it does.

Treat those as a ceiling a custom QR stamp will never reach in the real world, not a target. One payload, one decoder, one clean render, and no ink in any of it. The budget this page holds you to is 60 percent of the published capacity for exactly that reason: the smudges, the half-pressed corner and the phone held at an angle all come out of the same account, and they have not been charged to it yet.

The other half of the answer is where the plate sits rather than how big it is. The three heavy squares in the corners, their white separators, and the two dotted lines running between them are function patterns. A reader uses them to find the code and work out its grid before it decodes anything, so they are not covered by any correction level. Some readers cope with a nick out of one, so this is not a guarantee of failure, but moving from L to H buys you exactly nothing here, which is the part worth knowing. The plate on this page is capped so it cannot reach them.

There is a fourth kind, and it is the one that catches people out. Alignment patterns show up from version 2, and their job is to let a reader unwarp a picture taken at an angle. For small symbols there is one, and it sits down in a corner where nothing disturbs it. From version 7 they start landing near the middle instead, which is exactly where a centre plate goes. A long payload such as a full contact card needs a symbol that size, so on those designs a centre plate lands on one no matter how small you make it. That is not automatically fatal. A decoder looking at a flat scan usually copes; a phone held at an angle over a stamped page, which is the normal way one of these gets read, copes less well. The builder says so when it happens rather than quietly letting it through, and the honest fix is a shorter payload rather than a smaller plate.

Denso Wave states the requirement in one sentence: a QR code requires a four-module wide margin at all sides of a symbol. It is not padding and it is not taste. A reader uses the empty band to tell where the code stops, and a design that crowds a ring or a line of text up against the last row of modules has taken part of the code away without touching a single module.

This is the most common way a custom QR stamp fails, because a stamp frame is a ring or a box drawn around something, and the natural instinct is to close the gap and make the artwork look tight. So the 4 module margin is not a control on this page. It is built into the layout, the frame is placed outside it, and the preview shows you the real proportion rather than a flattering one.

The text stamps on this site offer a warm oxblood because it looks like a stamp should look. On a code it is the riskiest thing on the panel. A reader works on light against dark, and that red measures 5.9:1 against white paper where the near black measures 18.9:1. Both scan off a clean white sheet in good light. Only one of them still scans off a kraft mailer, under a warm bulb, through a phone camera that has decided to expose for the room.

Each ink swatch reports its own ratio, and a custom QR stamp under 7:1 gets flagged even when the geometry is perfect. The ratio is borrowed from the accessibility standard rather than the QR one, which asks for dark on light without naming a number, so use it to compare inks against each other rather than as a pass mark. The comparison is the useful part.

One more decision the tool makes for you. The exported PNG has white paper under it, while the SVG stays transparent. A transparent code dropped onto a dark background inverts, and an inverted code fails silently, so the raster export you are most likely to paste into a document carries its own background. The vector one does not, because that file is going to a die cutter who wants the shape.

The symbology has no minimum physical size, which is technically true and practically useless. What has a minimum is your die. Below roughly 0.5mm a module, ink creeping sideways out of the relief starts closing the light squares, and a closed light square is a wrong module rather than a dirty one. Correction can argue with dirt. It cannot argue with the code saying something else.

The arithmetic is short. Modules across, including both margins, times your floor. A short asset id at level H needs 37 across, so around 19mm of stamp. A full contact card at the same level runs past 60 across, so past 30mm, which is a large stamp to press by hand. That is the real reason to think about what you encode: a shorter payload is not tidier, it is physically smaller, and the builder above recalculates it while you type.

Two ways out when a custom QR stamp comes back too big to press by hand. Encode a short link on your own domain rather than a tracking URL with forty characters of campaign parameters, or drop from H to Q and accept a smaller margin for error. The tool will tell you what each one buys.

Four jobs come up over and over, and each one wants something different from a custom QR stamp.

Inventory and asset tagging

The easiest case, because an asset id is short, so the code is sparse and the stamp can be small. The rectangular frame suits it: code on the left, department and owner beside it in plain text, so a person can read the tag without a phone. Level H, dark ink, and stamp onto a white label rather than the equipment.

Event check-in

Read once, indoors, off a clean badge, by a phone held six inches away. This is the one case where Q is genuinely enough and the extra density of H buys you nothing. Keep the code and the event name on the same face so a stack of unstamped badges cannot be confused with a stamped one.

Business card seals

A vCard encodes a whole contact record, which is a lot of characters and a dense code. Either accept a wide stamp, or encode a link to your own page instead and let the phone fetch the details. The second option makes a far smaller code and survives you changing phone number, which the first one does not.

Document authentication

A code that points at a record on your own site, stamped on the paper copy. This is the case with the longest life: the page will be filed, photographed, photocopied and read back in two years, and every one of those steps spends part of the correction budget. Level H, no overlay, the darkest ink, and a URL short enough to keep the module size comfortable.

A custom QR stamp from this page is artwork. It is not a physical stamp, we do not sell one, and we do not know what your manufacturer's frames measure. It does not track scans, and the code it draws is static, so the destination is baked into the pattern and cannot be edited afterwards. If you need to change where it points, put a redirect you control in the middle.

It also cannot promise your custom QR stamp will scan. Nothing that draws a picture can. What it can do is refuse to draw the designs that certainly will not, tell you which budget you are spending, and be honest that the last stretch of that budget belongs to the ink and the hand rather than to the code. Press a test sheet on the stock you will actually use, scan it with the oldest phone in the office, and only then approve the die.

Two smaller limits. The stamp is drawn in Georgia rather than the display face used elsewhere on this site, because an exported file that references a webfont it cannot carry arrives looking nothing like the preview, and wherever the SVG is opened without Georgia the viewer will substitute something else. And the correction levels are the four the standard defines, so if you were hoping for something between Q and H, there is nothing there to offer you.