The ultimate guide to reading a bar code

bar code

UPC barcodes typically encode the identity of a company that manufactures or sells the product, along with the code that the company has assigned to the specific product. In rare cases, you can find a little more information by reading the 12 digits. Otherwise, you can just impress your friends by learning to actually convert the bars and spaces in a barcode into numbers. Have them cut or hide the numbers at the bottom of a UPC barcode, then “read” them the numbers by looking at the bars.

Interpret the 12 printed digits on a barcode

For most 12-digit codes, you can look up the barcode online.

The UPC code encodes only a manufacturer’s identity and a number identifying each product, except in specific cases described in the following steps. In most cases, however, no additional information is included in the UPC code, so there is nothing to be gained by trying to read the barcode yourself. Instead, you can look it up online using a free service like that of GTIN, the site of the official agency that issues barcodes in the US, or, a database created by private users. Enter the full 12-digit barcode in the “GTIN” or “Search for a product” field. There are a few exceptions, detailed in the next step, where you can find more specific information. GTIN stands for Global Trade Item Number, a data system that also includes UPC. 12-digit UPC codes are also known as GTIN-12, UPC-A or UPC-E.

Understand the basics of barcodes.

While a 12-digit barcode doesn’t contain much human-readable information, you can still learn about how it works. The first 6-10 digits of a 12-digit barcode reveal the company that makes or sells the product (both companies can choose to put a barcode on their product). This code is issued and sold on application by a non-profit organization, GS1. The remaining digits, except the last one, are thought up by the company to describe each of its products. For example, a company may be assigned the code 123456. It can then print any 12-digit barcode starting with 123456 and create one for each of its products. Compare two barcodes from the same company to see if you can find the company’s barcode. The purpose of the last digit is explained later in this section.

Learn how to interpret a barcode whose first digit is a 3.

Drugs, pharmaceutical products, and occasionally beauty products, commonly have barcodes that start with a 3. The next 10 digits are the National Drug Code number. The process of converting a National Drug Code to a barcode can introduce ambiguity, so it’s not always possible to read the code from a list of drug codes. Instead, you can look up the code on an NDC code search engine. This type of 12-digit number is sometimes referred to as a UPN, Universal Product Number. Although drug identifiers are always 10 digits long, they can contain dashes (or spaces) that are not displayed in the barcode. For example, 12345-678-90 and 1234-567-890 are two different codes for drugs, but only one of them can use the same sequence of numbers as a barcode.

Understand barcodes with a 2 as the first digit.

These barcodes are given to items sold by weight. Usually, the first six digits, including the 2, indicate the manufacturer of the product, and the next five followings are used locally by the store or warehouse to indicate the weight of the product or the price for a given weight. If you have multiple products from the same location but with different weights, you can try to find the code for a specific weight. Unfortunately, the system is left to each warehouse or store, so there is no universal code to interpret. Enter the full barcode in GSI’s search option in the “GTIN” field to find the manufacturer. It will also show you which part of the barcode is the company’s prefix (usually the first six digits, but not always). The remaining digits (except the last one) should be the code representing the weight or price.

Learn more about the last digit.

The last digit is called the “check digit” and is usually determined from the preceding 11 digits using a mathematical formula. The purpose behind this is to detect misprints. While there are fake UPC barcodes, which are typically made by companies that don’t understand the need to apply for them, it would be easy to include the check digit, so it’s not a reliable way to find fake codes. (For this purpose, you should look up the code in the official database.) If you’re curious or like to do the math for fun, you can enter your barcode into a GTIN-12 check digit calculator, or follow the check formula yourself: add up the odd digits ( the 1st, 3rd, 5th, 7th, 9th and 11th digits). Multiply the result by 3. Add the new result to all the even-numbered digits (the 2nd, 4th, 6th, 8th, 10th, and 12th)—this includes the check digit itself. “Cross out” everything from your answer except the last digit, the number in the very last position. Subtract the new result from 10 and find the answer. For example, if the last step was an 8, you would calculate 10-8= 2. This result should now be the same as the 12th digit of your barcode.

Read UPC barcodes without the numbers

Understand the method.

Although barcodes are designed to be “read” by scanners and interpreted by computers, it is possible to practice looking at UPC barcodes and translating them into 12-digit numbers. This is rarely useful, especially since the 12 digits are printed under the barcode anyway, but you can learn it as a fun trick to show off to your friends or co-workers. Bar codes that are not used with the UPC system or use other digits cannot be read using this method. Most barcodes on products sold in the US and Canada are UPC barcodes, but be wary of compressed 6-digit UPC barcodes, which have a different, more complex encoding system.

Find three pairs of longer lines.

The barcode should be divided into three areas by a pair of longer lines. Look at the bottom of the vertical bars: some of the lines should go further down than others. There should be two longer lines at the beginning, two in the middle, and two at the end. They help the scanner read the barcode and are not translated into numbers. However, they have a purpose with this method: the bars to the left of the middle long lines can be read differently than those to the right. This is described in more detail below.

Recognize the four widths of the bars.

Each vertical bar (black or white) can have one of four different widths. From narrowest to widest, they are referred to as widths 1, 2, 3, 4 in this method below. Using a magnifying glass, if necessary, you can try to spot the differences in the width of the lines. Don’t confuse this designation with the numbers you’re actually trying to find, the numbers 1 through 4 simply describe the width of the bars.

Note the width of the bars on the left.

Start with the bars on the left, between the long bars on the left and the long bars in the middle. Starting with the first white bar on the left, measure the width of each bar, black and white. Each digit of the 12-digit number is encoded using four bars. Write down the width of each bar, dividing them into groups of four bars. When you get to the extra-long bars in the middle, you have six groups of four digits each. For example, if the first bar after the extra-long lines on the left is the narrowest width, write a 1. Then, when the right bar next to it has the widest width, write down a 4. If you did this for four bars (black and white), leave a space before noting the next bar. For example, if you wrote “1422,” move to the next line to write the next bar width.

Do the same on the right side, but start with a black bar.

Don’t decipher the particularly long bars in the middle. Starting with the first regular-length black bar to the right of it, use the same method. This time, each group of four bars (representing a digit) has a black-white-black-white pattern. Stop when you have six more groups of four digits each and don’t decipher the extra-long bars on the right.

Translate the bar widths into real numbers.

Now that you’ve figured out which bars (of different widths) belong to which number, all you need to know is the code that translates these into real numbers in the 12-digit number. Use the following instructions: 3211 = 0 2221 = 1 2122 = 2 1411 = 3 1132 = 4 1231 = 5 1114 = 6 1312 = 7 1213 = 8 3112 = 9

Check your result.

If the numbers are printed under the barcode, read them to see if you made any mistakes. You can also lookup the product in GTIN’s database by entering the 12-digit barcode you found into the “GTIN” field. This is how you should find any company’s product that has been officially assigned a barcode, although companies sometimes print their own barcodes that are not found in the system. However, in most cases, the database should return a product name that matches the item you are viewing if you read the barcode correctly.

Read our blog to learn about how to read a bar code.


Karren Brandenburg

Karren Brandenburg is a travel and shopping expert. She has been quoted in Street Insider, Yahoo Finance, Reuters, ABC News, and MarketWatch. Karren has a total of 18 credit cards, using reward points to see the world on a budget.