What is the check digit?

The last digit is calculated from the others. Scanners use it to catch a misread, and if it does not match they reject the scan entirely rather than reporting the wrong number.

Is UPC-A the same as EAN-13?

Nearly. A UPC-A is an EAN-13 with a leading zero, and the bars are identical, which is why a European scanner reads an American product without being told anything.

Why will my printed barcode not scan?

Usually size or the margin. Print from the SVG at its intended size, keep the clear space either side, and use black on white rather than a colour.

UPC-A Barcode Generator

The North American retail barcode, eleven digits in.

Digits

Spaces and hyphens are ignored. Paste straight off a label.

Print the digits belowYes

Bar height60px

The North American retail barcode, eleven digits in.

How to use it

Enter eleven digits. The last digit is the check digit and is worked out for you. Paste twelve and it is verified instead.
Read the line under the code. It says whether the check digit was calculated or verified. If it does not match, the code is refused rather than drawn.
Download the SVG. Print it at the size you need. Scaling a bitmap barcode up blurs the bars and scanners give up.

When you would use this

UPC-A is the retail barcode used in the United States and Canada, twelve digits with the last calculated from the other eleven. Structurally it is an EAN-13 carrying a leading zero, and the bars produced are identical, which is why a scanner outside North America reads an American product without any special handling. The two ends of the number are printed outside the bars rather than under them, which is the visual difference people notice. As with every barcode in this family the check digit is the thing that matters: get it wrong and the symbol is drawn perfectly, prints perfectly, and fails at the till. It is calculated here when you supply eleven digits and verified when you supply twelve.

Questions

What is the check digit?: The last digit is calculated from the others. Scanners use it to catch a misread, and if it does not match they reject the scan entirely rather than reporting the wrong number.
Is UPC-A the same as EAN-13?: Nearly. A UPC-A is an EAN-13 with a leading zero, and the bars are identical, which is why a European scanner reads an American product without being told anything.
Why will my printed barcode not scan?: Usually size or the margin. Print from the SVG at its intended size, keep the clear space either side, and use black on white rather than a colour.