Making barcodes and QR codes, and fixing a rejected number

Most long reference numbers end with a check digit, worked out from the others, so that a typo is caught before the number is used. Barcodes carry one too. These tools find the mistake when a form says a number is invalid, make barcodes and QR codes for labels, stock and posters, and read them back.

The sections cover three separate jobs, so skip to the one you need:

• A number a form won’t accept: find the typo.
• Making a barcode or a QR code that scans, and testing it before printing.
• Where a QR code goes, before you open it.

1. A number the form won’t accept

Type it into Check Digit Validator. It checks IBANs, card numbers, ISBNs, ISSNs, barcode numbers, VINs, NHS numbers and more, and says which kinds it fits. When it fits none, each possible kind shows the check digit it would need: if that’s one digit away from what you typed, the mistake is often two digits swapped or one mistyped.

For a smudged or unreadable digit, type ? in its place, and every value that passes the check is listed; with one ? there’s usually just one. The same works for making the check digit of a new number.

A number that passes is well formed, not necessarily real: a valid IBAN can still be a closed account. Don’t use Copy a link to this input with a real card number, as the link keeps it.

2. Choosing a barcode

Barcodes makes five kinds. Pick by where it will be scanned:

• EAN-13 (or UPC-A in North America) for products sold in shops. Shops only accept numbers issued to you by GS1, the barcode standards body; a made-up number scans, but not as your product.
• EAN-8 for products too small for EAN-13, again with a number from GS1.
• Code 128 for your own labels: stock, asset tags, library books, parcels. It takes letters and numbers and needs no registration.
• Code 39 for older scanners and systems that ask for it. It’s wider, and capitals only.

For EAN-13, EAN-8 and UPC-A, type the number without its last digit and the check digit is added for you.

3. Making it print well

Download SVG stays sharp at any size, so use it for print; PNG suits a document or web page. A Bar width of 2 prints well at most sizes. Leave a clear margin of white either side of the bars, and print in black on white: scanners need the contrast, and red bars can’t be read by many red-light scanners.

4. QR codes

QR Code makes codes for a web address, any text, a Wi-Fi network that guests join by scanning, or a contact card that phones offer to save. Keep the text short: a long web address makes a dense code that’s hard to scan when printed small. Use a short address or a page that redirects, and Low or Medium error correction unless the code will be outdoors or likely to get scuffed.

5. Test it before you print a thousand

Take a screenshot or a photo of the code you made and read it back: QR Code reads QR codes in every browser, and Barcodes reads the other kinds in Chrome and Edge on Android, macOS and ChromeOS. Check that it says exactly what you meant, then scan a test print with a phone at the size it will really be.

6. Where does this QR code go?

QR codes on posters, parking meters and letters are a common way to send people to fake payment and login pages, as a code hides its web address. Take a photo or screenshot and read it in QR Code: the address is shown as text, with its host, and never opened. If the host isn’t the company it claims to be, don’t visit it. A Wi-Fi code is split into its network name and password.