Make a barcode: EAN, UPC, ISBN, Code 128

Which barcode to use

For your own labels, Code 128 is usually the best choice: it holds any plain text and packs digits tightly. Code 39 only has capital letters, so Octoolo turns lowercase into capitals and says so, and it can add the optional check character (modulo 43) with Add a check character.

Check digits, worked through

EAN, UPC, ITF-14 and ISBN-13 end with a check digit, so a scanner can tell when a bar was misread. To work it out, take the digits before it from the right, multiply them by 3, 1, 3, 1 and so on, add them up, and take what is needed to reach the next multiple of ten. For 590123412345:

5×3 + 4×1 + 3×3 + 2×1 + 1×3 + 4×1 + 3×3 + 2×1 + 1×3 + 0×1 + 9×3 + 5×1 = 83, and 90 − 83 = 7, so the EAN-13 is 5901234123457.

Type the 12 digits and Octoolo adds the 7. Type all 13 with a wrong last digit and it says “The last digit should be 7, not 0”. UPC-E is checked through the 12-digit UPC-A number it stands for: 425261 becomes 04252614, with the number system 0 at the front and the check digit 4 at the end.

ISBNs work the same way. An older 10-character ISBN is checked with its own rule (it may end in X) and turned into the 13-digit one: 0-306-40615-2 becomes 978-0-306-40615-7, with 978 in front and a new check digit. The ISBN is printed above the bars as books show it, keeping the hyphens you typed.

Printing barcodes that scan

• Size. At 100% size the narrowest bar of a shop barcode is 0.33 mm, and retailers accept roughly 80% to 200% of that. For print, save an SVG, or a PNG at 4×, and place it at a size where the bars stay crisp.
• Quiet zone. Scanners need blank space on both sides. Keep the Quiet zone and leave room around the code on the label.
• Colors. Dark bars on a light background. Black on white is safest; red bars do not scan, because many scanners use red light.
• Height. Short codes are harder to scan at an angle; lower the height only when the label demands it.
• Test it. Print one and scan it with the scanner or phone app that will read it before printing a thousand.

One thing a generator cannot do is give a product a number. Barcodes on goods sold in shops use numbers licensed by GS1, the organization that runs the EAN and UPC system; making up a number risks clashing with another product. For your own stock, events and documents, any Code 128 text is fine. For links, a QR code holds far more than a barcode.