What Is a Barcode?
Definition
A barcode is a visual, machine-readable representation of data that a scanner can read far faster than a human eye. At its simplest, it is a number or piece of text translated into a pattern of bars and spaces (or squares).
"Barcode" is a general term covering both one-dimensional (1D) line codes and two-dimensional (2D) symbols. A barcode carries no meaning on its own; the system that reads it decides what the encoded number represents.
You don't need special hardware to read one; a phone camera is usually enough today. To see what a code contains, upload a photo to a tool like the image barcode reader.
1D vs 2D barcodes
1D (one-dimensional) barcodes include EAN-13, UPC-A, Code 128 and ITF-14. They are made of vertical bars of varying widths and usually represent only a number or short text, carrying data in a single horizontal direction.
2D (two-dimensional) barcodes include QR Code, Data Matrix and PDF417. Because they encode data both horizontally and vertically, they hold far more information in the same area; a QR code can carry hundreds of characters of URL or text.
A common misconception is that a QR code is separate from barcodes. In fact a QR Code is a type of 2D barcode; "barcode" is the umbrella term and QR is a subset of it.
Common barcode types
The most common retail type is EAN-13; nearly every product on a supermarket shelf carries this 13-digit barcode. In North America its counterpart is the 12-digit UPC-A.
In logistics and inventory, Code 128 dominates because it can carry alphanumeric data; it's common on shipping labels, warehouse shelves and internal tracking systems. For cases and cartons, the robust ITF-14 is preferred.
Once you've decided which type suits your products, you can produce a print-ready image with the barcode generator.
Common uses
Barcodes are used most in retail product labels, warehouse and inventory management, and shipping/logistics labels. Fast price lookups at checkout, stock counts and shipment tracking all become automated as a result.
Beyond retail they are everywhere: event and transit tickets, library books, hospital patient wristbands, asset tracking and restaurant menus are all common places to see barcodes and QR codes.
The common thread is this: a barcode is a way to link a physical object to a digital record quickly and without errors.
What readability depends on
Reliable scanning depends on size, contrast and the margin called the "quiet zone". Dark bars should sit on a light background, and there must be enough blank space on each side of the barcode.
Print quality is critical too: on a low-resolution printer, thin bars can merge, and a blurry print can fool a scanner. For thermal and laser printer settings, see barcode printing settings.
Always test a sample after printing; no tool can honestly promise a code scans "everywhere", but a well-produced barcode reads reliably on the vast majority of standard scanners.
Important limit
Generating a barcode does not mean the number is officially registered to a product or company. You can produce a valid barcode image with any tool, but that does not give you "ownership" of the number.
Products sold in retail chains need a unique, registered GTIN; those numbers are obtained by applying to an authority such as GS1. This site does not assign official GS1 numbers.
A number having a correct check digit only shows technical validity. To understand the concepts better, read what is GTIN and what is a check digit.