Barcode and SKU Systems for Inventory

Designing Your SKU System

A SKU (Stock Keeping Unit) is an internal code that uniquely identifies every product variation you sell. Unlike a UPC barcode, which is a universal product identifier used across all retailers, your SKU is your own system and can be structured however best serves your business. The purpose of a good SKU system is to let anyone in your operation identify a product at a glance: what category it belongs to, what the product is, and which specific variant (size, color, material) it represents, all from the code itself.

The most effective SKU format for ecommerce is a segmented alphanumeric code with 3 to 4 segments separated by hyphens. The first segment identifies the category or product line (2 to 3 characters), the second identifies the specific product (3 to 4 characters), and the third identifies the variant (2 to 4 characters). For example, a clothing store might use: AP-TSHRT-BLK-M for apparel, t-shirt, black, medium. A kitchen goods store might use: KT-CBOARD-BAM-12 for kitchen, cutting board, bamboo, 12 inch. Keep total SKU length under 16 characters so it fits on labels without wrapping and is quick to type manually when needed.

Rules for good SKU design: use only uppercase letters and numbers (no lowercase, no special characters other than hyphens between segments). Do not start SKUs with zero because some systems strip leading zeros. Avoid characters that look similar at a glance (O and 0, I and 1, S and 5). Never reuse a retired SKU for a different product because historical reporting and customer service lookups will return the wrong product. Document your SKU convention in a reference sheet that lists every abbreviation and its meaning so that anyone on your team can decode a SKU or create new ones correctly.

UPC Barcodes vs Internal SKU Barcodes

UPC (Universal Product Code) barcodes are the 12-digit codes used on retail products worldwide. If you sell on Amazon, in retail stores, or through wholesale channels, you likely need UPC codes for your products. Amazon requires a UPC, EAN, or ISBN for most product listings unless you have a brand registry exemption. Legitimate UPC codes must be purchased from GS1, the global standards organization, at a cost of $250 for an initial registration of 10 barcodes, plus a $50 annual renewal fee. Packages of 100 barcodes cost $750 initially. Third-party barcode resellers offer cheaper UPCs, but Amazon and major retailers increasingly reject resold barcodes that cannot be verified against the GS1 database.

Internal SKU barcodes are barcodes you generate yourself using your own SKU codes. These barcodes are not registered with any external organization and are only meaningful within your own warehouse operations. They are free to create and can encode any information you want: your internal SKU, a bin location, a lot number, or a combination. For warehouse operations like picking, packing, and counting inventory, internal SKU barcodes are all you need. You only need UPC barcodes for external-facing requirements: marketplace listings, retail distribution, and wholesale accounts.

Many sellers use both: UPC barcodes on their product packaging for marketplace and retail requirements, and internal SKU barcodes on their warehouse bin locations and internal product labels for operational efficiency. Your inventory management software maps the UPC to your internal SKU so that scanning either one identifies the product correctly in your system.

Generating and Printing Barcode Labels

Most inventory management platforms and shipping tools include barcode generation built in. Shopify generates barcodes for products when you enter a barcode value on the product page. Cin7, Ordoro, and Zoho Inventory all generate barcode labels that you can print directly. For generating barcodes independently, free online tools and desktop software like Avery Design and Print, Labelary, and the open-source Zint Barcode Generator create barcodes in common symbologies from any text input.

For barcode symbology, Code 128 is the best choice for internal warehouse barcodes. It is compact, supports the full ASCII character set (letters, numbers, and hyphens), and is universally readable by all modern barcode scanners. For product-level UPCs, the UPC-A symbology is standard in North America, and EAN-13 is standard internationally. Your barcode generation tool will produce the correct symbology when you specify the barcode type and input the code.

Print barcode labels on a thermal label printer rather than an inkjet or laser printer. Thermal printers produce crisp, high-contrast barcodes on adhesive labels at 2 to 5 cents per label, and they never need ink or toner because they use heat to create the image on thermal label stock. The Rollo 4x6 thermal printer ($200) and DYMO LabelWriter 4XL ($250) are both popular choices for ecommerce operations. Direct thermal labels can fade if exposed to heat or sunlight, which matters for product-facing barcodes but is not an issue for warehouse bin labels in a controlled environment. For labels that need to be durable and heat-resistant, thermal transfer printers use a ribbon to produce more permanent prints at a slightly higher per-label cost.

Barcode Scanner Hardware

A basic USB barcode scanner costs $30 to $80 and connects to your computer like a keyboard. When you scan a barcode, the scanner types the barcode's content into whatever field is active on your screen, exactly as if you had typed it on your keyboard. No special software is needed for this basic functionality. Popular entry-level models include the Tera HW0002 ($35), the Inateck BCST-70 ($40), and the Netum C740 ($30). All of these read Code 128, UPC-A, EAN-13, and other common symbologies out of the box.

Wireless scanners ($50 to $150) connect via Bluetooth and are essential for picking operations where you move through the warehouse away from a fixed computer. The scanner stores scans in a buffer and transmits them to a base station or paired mobile device. Some models have a range of 30 to 100 feet, which covers most small to medium warehouse layouts. For larger operations or environments where Bluetooth range is insufficient, consider a mobile computer with an integrated scanner, such as the Zebra TC21 or TC26, which combines a touchscreen, wireless connectivity, and a built-in barcode reader in a handheld device that runs your inventory management app directly.

2D barcode scanners ($40 to $100) read both traditional 1D barcodes and QR codes or Data Matrix codes. If you ever need to encode more information than a simple SKU (lot numbers, expiration dates, serial numbers), 2D barcodes can hold significantly more data in the same label space. For most ecommerce warehouses, a basic 1D scanner covers all needs, but spending the extra $10 to $20 for a 2D scanner provides future flexibility.

Integrating Scanning Into Your Workflow

The highest-impact use of barcode scanning in ecommerce is pick-and-pack verification. When a picker retrieves a product from a shelf, they scan the product barcode and the system confirms it matches the order. If the wrong product was picked, the system rejects the scan with an audible alert. This single check prevents the most expensive warehouse error: shipping the wrong product. A mispick that reaches a customer costs $15 to $40 in return shipping, replacement shipping, re-stocking labor, and potential negative reviews. Even at a modest 1% manual error rate, a warehouse shipping 200 orders per day sends 2 wrong packages daily, costing $30 to $80 per day in avoidable expense.

Receiving verification is the second most valuable scanning application. When a supplier shipment arrives, scan each product as you count it and compare the scanned count against your purchase order. This catches quantity discrepancies, wrong products, and substitutions at the point of receiving rather than weeks later during a cycle count. If your purchase order is for 500 units of SKU KT-CBOARD-BAM-12 and your scan count shows 485, you immediately know to record 485 in your system and follow up with the supplier about the 15-unit shortage.

Cycle counting with barcode scanning is faster and more accurate than manual counting. A warehouse worker walks the aisle, scans each bin location, scans the product in that bin, and enters the physical count. The system compares the scanned count to the expected count and flags any discrepancies for investigation. What might take 4 hours as a manual count-and-record process takes 1 to 2 hours with barcode scanning, and the data goes directly into your inventory system without manual data entry errors.