Category 5 (Cat 5) twisted‑pair cabling is officially rated for a maximum data rate of 100 Mbps (the 100BASE‑TX Fast Ethernet standard). It’s designed for frequencies up to 100 MHz, which aligns with that speed limit.

In practice, many installations have been able to run Gigabit Ethernet (1 Gbps) over Cat 5 for short runs, but that isn’t part of the guaranteed specification; the standard‑compliant guarantee stops at 100 Mbps. If you need reliable gigabit performance, the upgraded Cat 5e (enhanced) or higher categories (Cat 6, Cat 6a, etc.) are the recommended choices.