How to Read a Barcode Step by Step With Scanner, Phone, or by Eye

You see barcodes every day, but if someone handed you one and asked what it meant, would you know where to start? Scanning a barcode doesn't merely involve aiming a scanner and crossing one's fingers. There’s a system behind it, and it’s not hard to learn.

In this guide, I’ll show you three ways to read a barcode: with your eyes, with a scanner, and with your phone. For each one, I’ll walk you through how it works, when to use it, and what to watch out for. You’ll also learn what the numbers actually mean—and how to spot if something looks wrong.

How to Read a Barcode Manually (With Your Eyes)

You don’t need any devices to read a barcode—just your eyes and a bit of pattern recognition. Manually reading a barcode means looking at the black and white bars and figuring out what numbers they represent.

Initially, you'll notice the distinct lines indicating the start, center, and conclusion of the code. Then, you’ll look at the pattern of bars to decode each number. Ultimately, you'll verify the barcode's validity by computing the check digit. It takes a little patience, but once you understand the logic, it’s surprisingly satisfying—and a great way to learn how barcodes really work.

Step 1: Find the start, middle, and end lines

The first thing to notice in a barcode is the structure. Observe carefully, and you'll spot three clusters of elongated black lines: one positioned at the start, another in the middle, and the last at the close. These are called guard bars. They don’t contain data, but they show where the barcode begins and ends. Everything in between is where the real numbers are encoded.

These positions follow a fixed pattern: 101 at the beginning and end, and 01010 in the center. Scanners rely on these markers to know exactly where to start and stop.

Step 2: Understand how digits are encoded

Each number in a barcode is made up of two bars and two spaces, always totalling seven modules in width. The relative thickness of those four elements tells the scanner which digit it is.

These patterns are designed so that every digit adds up to seven units of width. For example, the number "3" might be represented as a thin black line, followed by a wider white space, then two more bars. You don’t need to memorize each pattern, but knowing that they follow a set system makes decoding easier.

There’s also a clever trick to how barcodes prevent errors: the left and right halves use different encoding formats. On the right side, the bar and space patterns are actually a mirror image—and even the black and white colors are reversed. This helps scanners know which direction the barcode is facing.

Step 3: Use a decoding chart (optional)

If you’re curious or want to try decoding a barcode yourself, you can use a UPC-A decoding chart. It shows which line patterns match which numbers. Compare each group of four bars in the barcode with the chart to find out the full number.

For example:

• 0 = 3211
  
• 1 = 2221
  
• 2 = 2122
  

Each of these refers to the relative widths of the black and white lines (3 units, 2 units, etc.), always totaling seven. It's akin to a concealed cipher hiding right out in the open.

It’s a bit like solving a puzzle—and once you try it, you’ll start to see the logic behind how barcodes are built.

Step 4: Calculate the Check Digit

The last number in the barcode isn’t part of the product information. It’s a check digit, used to make sure the barcode was read correctly.

Here’s how to calculate it:

• Sum the digits in the odd positions (e.g., 1st, 3rd, 5th), then multiply that total by 3.
• Next, tally the digits in the even positions (e.g., 2nd, 4th, 6th). Combine these two sums.
• Identify the smallest number to append to this combined total to reach the nearest higher multiple of 10. That number is the check digit.
  

Let’s say your total is 82. The next multiple of 10 is 90, so your check digit is 8. If the last digit in the barcode matches that, the code is likely valid.

The check digit helps catch scanning errors—but keep in mind, it can’t prevent counterfeits. A fake barcode can still pass this check, so it’s just one part of validating a product.

How to Read a Barcode Using a Scanner

Using a scanner is the fastest way to read a barcode—but it still helps to know what’s going on behind the beep. This method is simple: you’ll choose the right type of scanner, connect it to your device, scan the code, and then look at the number it gives you.

From there, it’s all about understanding what that number means—like where the product was registered, who made it, and whether the barcode is valid. Once you get the hang of it, scanning becomes more than just a quick action—it becomes a way to actually read and verify product info.

Step 1: Choose the right scanner

There are different types of barcode scanners, and each one has its own strengths:

• USB scanner – Great for desktops and checkout counters. Plug and go.
  
• Bluetooth scanner – Connects wirelessly to phones, tablets, or laptops. Good for moving around.
  
• 2D scanner – Can read QR codes and barcodes from screens or curved packaging.

If you’re not sure what to choose, start with a USB scanner. It works like a keyboard: you scan a code, and the numbers appear wherever your cursor is.

Step 2: Connect your scanner

Setting up a scanner is usually simple:

• For USB: Plug it into your device—it often works instantly.
  
• For Bluetooth:
  
  • Turn on Bluetooth on your device
    
  • Power on the scanner
    
  • Put the scanner into pairing mode
    
  • Select it from your device’s Bluetooth list
    

Once connected, you’re ready to scan.

Step 3: Scan the barcode clearly

Hold the scanner about 5 to 15 cm (2 to 6 inches) from the barcode. Make sure it’s well lit and fully visible. Avoid glossy surfaces that might reflect light.

Upon the scanner detecting it, you'll typically hear a beep or witness a light blink. That means the code has been successfully read.

Step 4: Get the output—and read what it means

Now the real reading begins.

The scanner will return a number—often a 12-digit UPC code or a 13-digit EAN code. Here's what to look for:

For 13-digit EAN codes:

• The first two or three digits usually represent the GS1 Prefix, which indicates the GS1 Member Organization where the manufacturer registered (e.g., 690–699 for GS1 China, 890 for GS1 India, 800–839 for GS1 Italy).
• The next set of digits is the GS1 Company Prefix (identifying the manufacturer).
• The following digits are the Item Reference (specific product code).
• The final digit is the check digit.

For 12-digit UPC codes:

• The first digit is the Number System Character (e.g., 0, 1, 6, 7, 8 for most products).
• The next five digits usually represent the manufacturer's identification number.
• The following five digits are the item number.
• The final digit is the check digit.

If you have an EAN-13 code like 6901234567892:

- 690 indicates the GS1 Prefix is for GS1 China.

- 12345 would be part of the GS1 Company Prefix.

- 6789 would be the Item Reference.

- 2 would be the check digit.

If you have a 12-digit UPC code like 071234567895:

- 0 is the Number System Character (typical for many retail products in the US/Canada).

- 71234 is the manufacturer's code.

- 56789 is the item number.

- 5 is the check digit.

You don’t need to memorize these rules, but if you often scan barcodes, it helps to recognize when something looks off—like a product labeled “USA” starting with a prefix that’s clearly not from the U.S.

Reading barcodes this way gives you more than just a string of digits. It helps you spot mistakes, verify product details, and understand the system behind the scan.

How to Read a Barcode with Your Cell Phone

Your phone can do more than just scan—it can help you actually read and understand a barcode. Whether you’re using an iPhone or Android, the process is simple: open your camera or a scanning app, point it at the barcode, and let your phone detect the code.

From there, you’ll see the barcode number—and with just a tap, you can look up what it means. You’ll find out where the product came from, who made it, and whether the code is valid. This method is especially handy when you’re shopping, comparing prices, or double-checking a product on the spot—no extra gear needed.

Step 1: Open your camera or scanning app

On the majority of iPhones and Android devices, simply launch the camera app and aim it at the barcode. A pop-up will appear once the code is detected.
If your phone doesn’t do this automatically, you can install a free barcode scanner app from the app store or Google Play.

Step 2: Point at the barcode

Hold your phone steady and keep the barcode centered in the frame. Ensure it’s adequately illuminated and clear of glare or obstructing shadows. Most cameras are quick to focus, but tilting slightly may help if it’s glossy.

Step 3: Wait for the pop-up

Once the camera detects the barcode, it’ll show you something—maybe a number, a product name, or a link to more information. That means the code has been successfully scanned.

Step 4: Tap to see more—and read the result

Tap the result to dive deeper. Many apps or camera integrations will show you:

• The barcode number (usually 12 or 13 digits)
  
• The product name
  
• The manufacturer
  
• The country prefix (based on the first few digits)
  
• Sometimes, price comparisons or links to retailer pages
  

That number isn’t random—it follows a structure, just like the one we explained earlier.
If it’s a UPC code (common in the U.S. and Canada), it will have 12 digits. If it’s an EAN (used internationally), it will likely have 13 digits. In many cases, you can convert a UPC into an EAN by simply adding a zero to the front.

Bonus Tip: What can you learn from the numbers?

Let’s say the barcode number is 8901234567890:

• 890 tells you the product is registered in India
  
• 12345 identifies the brand
  
• 67890 is the specific item
  
• And 0 is the check digit, used to make sure the code is valid
  

This means you’re not just scanning—you’re reading. You’re understanding how the product is categorized, where it comes from, and whether the code makes sense. Over time, you’ll start spotting patterns—and that’s when barcode reading becomes second nature.

How Barcode Numbers Work (And What They Mean)

Barcodes may look like a jumble of lines, but the numbers underneath follow a clear structure. Once you understand how these numbers are arranged, you can quickly spot patterns—and even check whether something looks off.

Let’s unpack a standard 12-digit UPC (Universal Product Code). It’s the most common barcode format in the U.S. and Canada.

Here’s what each part usually means:

• First 6 to 10 digits (the GS1 company prefix): Manufacturer code — this tells you who made the product
  
• Next 5 digits: Product code — a unique ID for that specific item
  
• Last digit: Check digit — used to confirm the code is structurally valid
  

For example, if a barcode reads 690123456789, here’s how to interpret it:

• 690 tells you the product was registered in China
  
• 12345 identifies the brand or company
  
• 6789 is the product identifier
  
• 9 is the check digit, calculated based on the other numbers
  

Even though the barcode doesn’t show product details directly, it’s a shortcut into product metadata.

What’s a check digit, really?
It’s a built-in way to detect scanning errors. If one number gets misread, the check digit calculation won’t add up—and that alerts the system.

UPC vs. EAN: What’s the Difference?

If you’re scanning a barcode outside North America, chances are it’s an EAN (European Article Number), not a UPC. The format remains largely identical—save for an additional digit at the outset:

• EAN barcodes have 13 digits
  
• They often begin with a country prefix, like 890 for India or 800 for Italy
  
• UPC barcodes can be converted into EAN by simply adding a 0 at the front
  

For example:

• UPC: 012345678905
  
• EAN: 0012345678905
  

Both work the same way—they just follow different registration systems.

Special Prefixes and What They Mean

Most barcodes follow a standard pattern—but some prefixes tell you more than others. Here are a few examples:

• 2 → Products sold by weight, like produce or bulk goods. The rest of the code usually relates to weight or price.
  
• 3 → Pharmaceuticals or health-related products. Often tied to National Drug Codes (NDC).
  
• 0 / 1 → Regular retail products.
  

This is helpful when checking if a product’s label matches what its code implies. For example, a bag of apples with a prefix of 2 makes perfect sense—but a tube of toothpaste probably shouldn’t start that way.

Once you know how to read barcode numbers, you can do more than just identify a product. You can spot formatting issues, recognize product categories, and even catch codes that look suspicious. It’s a small bit of knowledge that can give you big insight.

Tools to Help You Read or Create Barcodes

If you don’t want to decode barcodes by hand, there are simple tools that can help.

You can upload an image of a barcode to an online reader and get the number instantly—useful for digital files or when a scanner isn’t available. If you need to generate your own barcodes, free tools let you enter text or numbers and download a scannable image. You can even use spreadsheet software like Excel with barcode fonts or add-ins to create and manage codes for products or inventory.

These utilities are user-friendly for novices and demand no coding expertise. They’re perfect for exploring barcodes or organizing things more efficiently.

What is the easiest barcode to read?

The UPC barcode is generally considered the easiest to read. It has a simple 12-digit structure, is widely supported, and doesn’t include special characters or complex formatting.

What is the first two digits of a barcode?

For 13-digit EAN (GTIN-13) barcodes, the first 2–3 digits are the GS1 Prefix, showing the GS1 Member Organization where the barcode was registered (e.g., 690–699 for GS1 China). It indicates registration, not where the product was made.

For 12-digit UPC (GTIN-12) barcodes, the first digit is the "Number System Character" (e.g., '0', '1', '6', '7'). UPCs are mainly used in the U.S. and Canada. When used internationally as part of the EAN system, a '0' is added to make it 13 digits, and the GS1 prefix (e.g., '00'–'13') shows GS1 US or GS1 Canada registration.

What colors cannot be used with barcodes?

Red—and other warm hues rich in red, orange, or yellow—should never be used for the bars because red-light lasers see them as ‘white’. Stick to dark, cool colours (black, navy, dark green) for the bars and keep the background light.

How can you distinguish if a barcode is Code 128 or Code 39?

Look at the character set. Code 128 supports all ASCII characters and is compact. Code 39 only uses uppercase letters, numbers, and a few symbols. Code 128 usually has more bars packed into a shorter space.

Do barcodes read black or white?

Scanners don’t "see" colors. They identify the disparity between light and dark tones. It’s the black bars on a white background that matter most.

What makes a barcode unreadable?

• Low contrast (e.g. red on white)
  
• Blurred or smudged printing
  
• Wrinkled or damaged packaging
  
• Glare from glossy surfaces
  

Final Thoughts on Learning to Read Barcodes

You don’t need special gear or technical training to read a barcode—you just need to know what to look for. Whether you’re using your eyes, a scanner, or your smartphone, the steps are surprisingly simple once you break them down.

Now that you’ve seen how barcodes are structured and what the numbers actually mean, you’re no longer just scanning—you’re decoding. You can tell where a product was registered, who made it, and whether the code is valid.

So next time you see one of those black-and-white stripes, don’t just walk past—stop and read it. Try scanning something nearby. Look at the numbers. Check the country code. Calculate the check digit just for fun.

It may appear trivial, but once you spot the hidden logic in every barcode’s design, you’ll forever see product labels through a new lens. And who knows? You might even impress someone while you’re at it.