Electronic Devices: How Upc Bar Codes Work

UPC bar codes are found on most retail items. It's easy to see how they work and know what the different parts mean.

UPC stands for Universal Product Code. A UPC bar code is only one specific type of bar code among many others. UPC bar codes are typically used to identify retail items or products, as its name implies. Virtually any item that is bought in a retail store will have a UPC bar code on it.

UPCs consist of two slightly different parts. First is the UPC bar code itself, consisting of a set of bars. Second is the numbers under the barcode. These two parts are both the UPC. They convey the same set of information, just in different manners.

In UPC code, the numbers 0-9 are each represented by a different section of bars and the corresponding spaces between the bars. Each number consists of seven units. The string of numbers is essentially the same as the set of symbols in the UPC bar code. The numbers are there in case they are needed. For example, if the bar code does not want to scan in for some reason, the numbers allow the UPC to be entered manually. Each number is determined by the size and order of the bars in the section.

In fact, by looking at a few different UPC labels you can learn which sets of bars go with which numbers and read them without the numbers. When doing this, note that a UPC bar code begins and ends with a set of two thin bars separated by a thin space, with a space on the inner side of it. These two thin lines also appear in the center of the UPC bar code, a single space on either side of them.

If you try figuring the numbers out from the code, it will help you to know that the numbers on each side of the center set have a different set of codes that represent the numbers. Across the center line, bars become spaces and spaces become bars. This means that even if you don't know what a 6 looks like on the right, you can take the inverse of what a 6 looks like on the left.

The UPC bar code is scanned using a scanner or reader that uses light to read the widths of the bars and space between them. The scanner determines the barcode and a computer or cash register then matches it with the number associated with an item. During checkout, once the number is recognized, the price is then pulled from that description, not the barcode itself. This means the same item can be charged at a different price at different stores.



Many UPC bar codes in the US and Canada are 12 characters. This is UPC version A. Some UPCs are shorter than these 12 digits. Some items have UPCs consisting of only 8 characters. This shorter version uses zero-suppressed numbers. This allows a barcode such as 044000 001235 to be reduced to 04412305.

So what do the numbers mean?

The first six digits listed are the manufacturer's identification number. This number is obtained through the UCC (Uniform Code Council) and assigned to the manufacturer.

The first of these six digits tell a little about the item the bar code is on. For example, 0, 6, 7 indicate a standard UPC number. All zero suppressed UPCs begin with 0. UPCs starting with 2 are often fresh fruits, vegetables, and other food measured by weight. The number 3 usually represents pharmaceutical items, like shampoo and conditioner. UPCs beginning with 4 are in-store coupons and will only be recognized and make sense to the store that made them. Most other coupons, such as manufacturer's coupons, begin with 5.

The next five digits are the specific item's identification number.

Finally, the last digit is the check digit. This last digit lets the scanner know if the UPC code was scanned in correctly, and the scanner finds this digit whenever an item is scanned. For example, using the UPC bar code 05432100089?, where ? represents the check digit, one can easily perform the calculation the scanner uses to check the code.

To find the check digit, first add all the numbers in odd positions in the UPC. These will be the 1st, 3rd, 5th, 7th, 9th, and 11th digits.

0 + 4 + 2 + 0 + 0 + 9 = 15

Next, multiply the resulting number by 3.

15 * 3 = 45

Now, you would take all of the numbers in even digit positions, ignoring the check digit. These will be the 2nd, 4th, 6th, 8th, and 10th digits.

5 + 3 + 1 + 0 + 8 = 17

Add the two results together.

45 + 17 = 62

Now, to find the check digit, find the number needed to make this sum divisible by 10.

62 + 8 = 80

The check digit is 8, making the full UPC bar code 054321000898.

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