A 1D barcode, also called a linear barcode, encodes data as a series of parallel lines (bars) and spaces of varying widths arranged horizontally. The ratio of bar-to-space widths, and the overall pattern, determines the encoded value. Because data is encoded in only one dimension (left to right), 1D barcodes have a relatively low data density compared to 2D symbologies, but they are extremely fast to decode, have been in use for over 50 years, and are universally supported by virtually all barcode readers. Common 1D symbologies include UPC-A, EAN-13, Code 128, Code 39, ITF-14, GS1-128, Codabar, and Code 93.

Code 128 is the most versatile 1D symbology, capable of encoding all 128 ASCII characters at high density, making it the dominant choice for shipping labels, inventory labels, and GS1-128 applications (where it carries Application Identifiers such as lot numbers, expiration dates, and serial numbers). Code 39 is older and less dense but still widely used in automotive, defense, and healthcare because it does not require a check digit and is easy to print on low-resolution printers. ITF-14 (Interleaved 2 of 5) is used for outer carton labeling in retail supply chains. Each symbology is defined by an ISO/IEC standard that specifies the exact bar/space ratio rules, quiet zone requirements, and character set.

1D barcodes are the right choice when data volume is small (12–48 characters is typical), when laser scanners are already deployed (laser scanners cannot read 2D barcodes), and when label area is not a constraint. A Zebra ZD421 direct thermal printer produces crisp Code 128 labels at 203 dpi suitable for carton labeling, while a Honeywell DS2208 presentation scanner reads 1D codes at up to 270 scans per second for high-throughput checkout lanes. When data density exceeds what a 1D code can hold, or when omnidirectional scanning is required, consider upgrading to a 2D symbology.