The number
How a UPC-A number is built
UPC-A carries twelve digits, formally a GTIN-12. The first is the number system digit, which signals what kind of item you are looking at: 0, 1, 6, 7, 8 and 9 are ordinary retail goods, 2 is reserved for variable-weight items priced in store, 3 marks drugs and health items carrying an NDC, 4 is for retailer in-store use, and 5 is for coupons.
The digits after it split into a company prefix and an item reference, exactly as in EAN-13, with the split point decided by the size of the licence. The last digit is the mod-10 check digit.
The visual layout is distinctive: the first and last digits sit outside the guard bars in smaller type, and their bars are printed at full height alongside the guards. That is not a stylistic choice — it is part of the specification, and the generator draws it that way automatically.
The useful fact
UPC-A is EAN-13 with a leading zero
Encode 036000291452 as a UPC-A and encode 0036000291452 as an EAN-13, and you get an identical pattern of bars. UPC-A is a strict subset of EAN-13, which is why any modern scanner reads both and why marketplace databases store both forms of the same product.
This matters in two practical ways. First, if a supplier sends you a thirteen-digit number that begins with zero, you can drop the zero and treat it as a UPC without changing anything. Second, if a listing form insists on twelve digits and your number has thirteen with a leading zero, you are not stuck — it is the same product identifier.
The reverse is not true. A thirteen-digit number that begins with any digit other than zero cannot be shortened to a UPC-A, and there is no way to make it fit a twelve-digit field.
Printing
Size, placement and colour
Nominal UPC-A is 37.29 mm × 25.91 mm at an X-dimension of 0.33 mm, and the permitted range runs from 80% to 200% of that. Below 80% you are asking a scanner to resolve bars thinner than 0.264 mm, and the failure rate climbs quickly.
Place the symbol on a flat panel rather than across a seam, a fold or a curve tighter than about 30 mm in diameter. Keep it out of the bottom 8 mm of a package where conveyor rollers and grippers scuff labels. Print dark bars on a light background: black on white is ideal, dark blue or dark green on white works, and red bars on white do not work at all because a red laser sees red as white.
Selling online
UPCs on Amazon and other marketplaces
Large marketplaces validate the numbers you submit against the GS1 registry. A syntactically valid UPC with a company prefix that does not belong to you will be rejected, and repeated attempts can put a seller account at risk. If you are creating listings for products you manufacture, license a prefix; if you are reselling, use the manufacturer's existing number rather than minting a new one.
Where this tool earns its keep is everything after that: turning a number you already own into a clean, correctly proportioned symbol for your packaging artwork, your shelf labels or your product photos, without a subscription or a watermark.
Questions
Frequently asked questions
What is the difference between UPC and EAN?
UPC-A holds twelve digits and is the North American retail standard; EAN-13 holds thirteen and is used elsewhere. A UPC-A is the same code as an EAN-13 that starts with zero.
Can I make a UPC-E short code here?
Not yet. UPC-E compresses certain UPC-A numbers with runs of zeros into eight digits for small packages. Only numbers with the right zero pattern can be compressed.
Is a free UPC number legitimate?
Numbers resold cheaply usually come from prefixes issued to another company before 2002. They often scan, but marketplaces increasingly reject them because the registry shows a different owner.
Does the check digit have to be printed?
It is part of the number, so it is encoded in the bars and printed in the human-readable line beneath. You cannot leave it out.
What size should a UPC be on a small bottle?
Do not shrink below 80%. If a full UPC-A will not fit, license an EAN-8 or use a UPC-E number, both of which are designed for small packaging.
Can I put a UPC on my own homemade labels?
For your own stock control, absolutely. For anything scanned at a retailer, you need a number licensed to you.