The barcode appears here
Draws a barcode for each line: 13 digits as EAN-13, 12 as UPC-A, 8 as EAN-8 and 14 as ITF-14. If the last digit isn't the right check digit, the barcode gets the right one and the strip above it says which digit changed, so a typo doesn't end up on a label unnoticed. Download saves the barcode on screen as a PNG; All puts the whole list on one image.
Auto reads the format from the number of digits:
Pick a format above and it is used for every line: a number that doesn't fit it is listed with the reason instead of being drawn.
Bar width is the number of pixels for the narrowest bar, so it sets the size of the PNG. Raise it for a bigger image rather than stretching a small one, which blurs the bar edges. Keep the margin as well: scanners need blank space on both sides of the bars.
The PNG is an image of the number, nothing more. GS1's General Specifications (under References) set the sizes allowed for retail barcodes, so print one and scan it before you print a batch.
A barcode only draws a number; it doesn't register one. A product number for retail comes from a GS1 company prefix licensed to you, and the Barcode Calculator adds the check digit to each new number. To check numbers you already have, use the Barcode Validator.
For Data Matrix or an Avery label sheet, use the EAN Check barcode generator.
Get a product number on your own GS1 prefix, then draw and test the barcode.
Because it wasn't the check digit the other digits make. In Auto the barcode is drawn with the right one, and the strip above it says which digit changed. Treat it as a warning: a wrong check digit usually means a typo, and if the typo is earlier in the number, the corrected barcode belongs to a different product. Check the number at its source before you print.
Both carry a 12-digit GTIN-12 and both are used in the US and Canada. UPC-A prints all 12 digits; UPC-E is a shorter symbol for small packs that have no room for a full one. This page draws UPC-A, not UPC-E.
A barcode for text: letters, digits and symbols, at any length, which is why SKUs, lot numbers and shipping labels use it. It isn't for products at a checkout; those take EAN-13 or UPC-A. GS1-128 is Code 128 with GS1's data fields, such as (01) before a GTIN. This page draws plain Code 128.
Big enough that every bar prints cleanly. For retail barcodes, GS1's General Specifications set the sizes allowed. Here, Bar width is the pixels per narrowest bar: raise it for a bigger image instead of stretching a small PNG, which blurs the edges. Keep the margin too, since scanners need the blank space. Then print one and scan it before you print a hundred.
