USB-A
USB · 4 specs
Direct Answer
USB-A (Standard-A) is the flat rectangular connector on host ports -- computers, chargers, hubs. It used 4 pins for USB 1.x/2.0 speeds; a 9-pin variant, adding 5 SuperSpeed contacts, extended it to USB 3.0+ in 2008 without changing the external shape or requiring a new socket design.
Source: USB-IF · Last reviewed Aug 28, 2026
Specs
| Pin Count | 4 (USB 1.x/2.0) or 9 (USB 3.0+, adds 5 SuperSpeed contacts) |
| Standard Base Dimensions | ~12 x 4.5 mm |
| Reversible | No |
| Typical Role | Host / downstream-facing port |
One Shape, Two Pin Counts
USB-A's external shell hasn't changed since the original USB 1.0 specification -- a deliberate design choice that let USB 3.0 host ports remain physically backward-compatible with older USB 2.0 and 1.x devices. The upgrade lives inside the shell: 5 extra SuperSpeed contacts sit behind the original 4 pins, used only when both ends of the cable and the port itself support USB 3.0 or later.
USB-A's most-cited usability complaint -- that it only inserts one way up, and rarely on the first try -- was a direct design driver behind USB-C's fully reversible connector roughly a decade later.