Half-width characters occupy half the horizontal space of full-width characters in monospaced fonts. Standard ASCII characters (A-Z, a-z, 0-9) and common symbols are half-width. Half-width katakana also exists in Japanese computing.

In Japanese web forms, users are often instructed to enter phone numbers, postal codes, and email addresses in half-width characters. Form UI design books discuss best practices for handling full-width and half-width input.

In UTF-8, half-width ASCII characters use 1 byte each. However, half-width katakana still uses 3 bytes, so it does not save storage space compared to full-width katakana.

Mixing full-width and half-width characters can cause bugs in programming. Programming fundamentals books cover character width as a basic concept.