What Is a Barcode and How Does It Work? A Guide for E-commerce Sellers

What Is a Barcode and How Does It Work? A Guide for E-commerce Sellers

If you sell products online long enough, those little scannable labels stop being background noise. At first, they feel like a technical checkbox. Something required so your listing can go live. Later on, they become the thing that decides whether inventory moves smoothly or grinds to a halt.

Most sellers don’t think much about product codes until something breaks. A listing gets rejected. A shipment gets flagged. A fulfillment center claims the item cannot be identified. That is usually when you realize these numbers matter more than expected.

Let’s take a look at what product barcodes are, how they function in everyday selling, and how online sellers should approach buying and using them.

What a Barcode Actually Represents

At its core, a barcode is a visual way to represent a product identification number so machines can read it quickly and consistently. The label itself does not contain product descriptions, pricing, or brand stories. It points to a record that already exists in a database.

When a warehouse worker scans a product, the system reads the code, checks the number, and pulls up the matching item record. If that number belongs to a different product or a different brand, confusion follows fast.

For online sellers, these identifiers usually take the form of UPCs or EANs. Those numbers tell marketplaces and logistics systems exactly what product they are dealing with.

When sellers say “my barcode caused a problem,” the real issue is almost always the underlying product number.

How Product Codes Are Read and Processed

Scannable labels work by translating visual patterns into digital data.

Traditional linear codes use a series of bars and spaces. Scanners shine light, measure reflections, and convert that pattern into numbers. Two-dimensional formats, such as QR codes, use grids instead of lines, which allows them to store more information in a smaller space.

Once scanned, the number is passed to the software. That software looks up the product in a database and returns the relevant details. This entire process happens in milliseconds.

Accuracy is the reason this system dominates commerce. Barcode scanning is widely cited as having an error rate of roughly one in 3 million scans. Manual data entry averages closer to one mistake per 300 keystrokes. That gap explains why fulfillment centers depend on scanning at every step.

Product Code Types Sellers Commonly Encounter

Most e-commerce sellers only deal with a handful of formats.

• UPC – Used primarily in the United States and Canada. This is the standard product identifier for consumer goods sold on major online marketplaces.
• EAN – Functionally similar to UPC, but more common outside North America. Widely accepted by global platforms.
• Code 128- Frequently used for internal tracking, warehouse workflows, and shipping labels. Sellers usually do not use this format as a public product identifier.
• QR codes – Often used for instructions, manuals, authentication, or marketing links. These are rarely accepted as primary product identifiers on marketplaces.

For most sellers listing physical products, UPCs and EANs are the ones that matter.

Buying and Generating Product Codes

This decision shapes how smoothly your catalog runs in the long term.

Getting numbers through GS1

GS1 is the organization that manages global product identification standards. When you purchase codes directly from GS1, your business is registered as the official brand owner.

Marketplaces check this ownership. Amazon, in particular, compares submitted product numbers against the GS1 database. If the registered brand name does not match the seller account, listings can be suppressed or rejected.

Industry research shows that more than 70% of major global retailers rely on GS1 standards to manage product data. That reliance explains why platforms have become stricter over time.

Buying from authentic sellers

On the other hand, many choose to buy barcodes from authentic sellers. They provide legitimate, unused product codes to those who want reliable product identifiers without unnecessary complexity. These codes are unique, traceable, and suitable for use on major marketplaces when sourced correctly.

Reputable providers are transparent about how their product numbers are issued and how they should be used. Clear documentation and consistency help prevent listing conflicts as a catalog grows.

Using reseller codes

Reseller numbers are cheaper because they were originally issued to another company and later resold. Some sellers use them without issues, especially in small catalogs.

The risks tend to appear later. Listings may get merged. Brand registry claims can fail. Product ownership becomes harder to prove. These problems often show up when you scale or introduce variations.

Creating internal scanning labels

For internal use, generating your own scannable labels is normal. Warehouses do this constantly for bins, pallets, internal SKUs, and shipping processes. These internal codes are not validated against global databases. They only need to work inside your systems.

Public product identifiers and internal tracking labels serve different purposes. Mixing them usually causes trouble.

Where These Codes Show Up in E-commerce

Once you start paying attention, you see these identifiers everywhere. They help marketplaces group identical products from different sellers. They allow inventory software to track stock levels accurately. Fulfillment centers use them to confirm picks, packs, and shipments.

Scanning during order fulfillment significantly reduces errors. Logistics studies often report error reductions of up to 90% when scanning replaces manual picking methods.

Shipping carriers rely on scannable labels to sort packages automatically. Returns processing uses the same system to identify items and route them correctly.

When these systems work, nobody notices. When they fail, everything slows down.

Placement and Print Quality Still Matter

A valid product number can still cause problems if the label is poorly printed or placed badly.

Common issues include low contrast, glossy packaging, curved surfaces, or labels wrapped across seams. These problems force manual handling at fulfillment centers. Industry estimates suggest that printing and labeling issues account for more than 25% of scanning failures in warehouse environments. 

Most of these issues are preventable. Flat surfaces, strong contrast, adequate sizing, and clear space around the code solve most scanning problems.

Product Codes vs SKUs

These terms get mixed up constantly.

Product codes identify items universally across marketplaces and retailers. SKUs are internal references created by sellers to manage inventory. One product can have one UPC or EAN and multiple SKUs. Customers never see your SKUs. Your systems depend on them.

Trying to replace product identifiers with SKUs almost always creates listing or fulfillment issues.

Problems Sellers Commonly Face

Some mistakes appear again and again. Using numbers already assigned to another product. Reusing the same identifier for multiple variations. Buying cheap codes from resellers and failing verification later. Printing labels too small to scan reliably.

These issues tend to surface as volume grows. Systems become less forgiving as scale increases.

Final Words

With newer technologies getting attention, scannable product labels can feel outdated. They are not. They remain fast, inexpensive, and deeply embedded in global commerce. They work across borders, platforms, and supply chains.

For online sellers, these identifiers determine how smooth daily operations feel. When done right, they fade into the background. When done wrong, chaos usually ensues. Understanding how they work and how to source them properly saves time, money, and stress as your business grows.