§ GUIDES
Guides from Barcode Press
How-tos, symbology references, and field notes on using barcodes well.
- Code 128 subsets, FNC1-FNC4, and the mod-103 check digitFull reference for Code 128: subsets A, B, C; FNC1 through FNC4; the mod-103 check digit with a worked example; the FNC4 + ISO/IEC 8859-1 Latin-1 extension. Sourced against ISO/IEC 15417:2007.
- EAN-13 structure and parity: how 13 digits fit in a 12-position symbolThe 95-module EAN-13 envelope, the L/G/R encoding tables, and the parity scheme that encodes the 13th digit without printing it. Includes the full G-code table, the left-half parity-pattern lookup, a worked decode of 5901234123457, and the GS1 prefix nuances most references skip.
- UPC-A complete reference: encoding, check digit, UPC-E, and the dead variantsThe 12-digit UPC-A symbol explained from modules to mod-10 check digit. Full L and R encoding tables, UPC-E zero-suppression rules with worked example, the UPC-B/C/D variants nobody uses, and where the GS1 prefix system actually came from.
- GS1 DataBar Explained: When It Replaces UPC and WhyThe seven DataBar variants, where they actually show up in the real world, and when to use DataBar instead of UPC-A.
- Do You Actually Need to Buy UPC Codes from GS1?The real answer on free vs paid UPCs, why cheap resold codes fail on Amazon and Walmart, and when a $5 UPC is genuinely fine.
- Code 39 vs Code 93 vs Code 128: The 1D ShowdownThree industrial 1D symbologies, one usually wins. Density, character set, check digits, and when to actually pick each.
- PDF417 vs Data Matrix vs QR: Picking a 2D SymbologyA practical three-way comparison of the 2D codes that matter - capacity, scan hardware, use cases, and how to actually choose.
- ITF-14 Explained: Shipping Carton Barcodes, GTIN-14, and SSCC-18What ITF-14 actually is, how it differs from GS1-128 and SSCC-18, and the size and bearer-bar rules that decide whether your case label scans.
- QR Code Size: How Small Can You Actually Go?The real math on QR code size, scan distance, and error correction - with a practical rule of thumb and the mistakes that make small codes unscannable.
- How to Print Barcode Labels That Actually ScanDPI, X-dimension, quiet zone, and the handful of print settings that decide whether your label works. A practical guide for anyone printing labels at real volume.
- UPC vs EAN: Which One Do You Actually Need?UPC-A and EAN-13 are the same standard with a different digit count. Here's how to pick the right one, when it matters, and when it doesn't.
- GS1-128 vs Code 128: Stop Confusing ThemGS1-128 and Code 128 look identical but mean very different things. Here's the actual difference, when each one is required, and which generator to use.
- Code 128 vs Code 39: Why Modern Retail Moved OnA technical comparison of Code 128 and Code 39 barcodes - character sets, density, check digits, and when each is the right choice. Code 39 has not disappeared, but there are very few good reasons left to use it.
- How the EAN-13 Check Digit Is Calculated (With a Worked Example)A complete walkthrough of the EAN-13 check digit algorithm, a worked example with a real barcode, why the check digit exists, and how the same algorithm underlies UPC-A, ISBN-13, and every GTIN format.
- Amazon FBA Barcodes: FNSKU vs UPC, and When to Use WhichA practical guide to Amazon FBA barcode requirements - what FNSKU and UPC are, how Amazon's 2026 policy change affects sellers, and how to decide which label goes on your products.
- QR Code vs Data Matrix: Which 2D Barcode Should You Actually Use?A practical comparison of QR Code and Data Matrix barcodes - capacity, error correction, physical size, regulatory requirements, and the one question that decides it: who is doing the scanning?
- Why Won't My Barcode Scan? A 7-Step ChecklistA systematic checklist for diagnosing barcode scan failures - covering quiet zones, contrast, print resolution, physical damage, wrong symbology, check digits, and scanner distance.