Network bandwidth oversubscription calculator

Oversubscription is the ratio of the bandwidth the connected devices could use to the bandwidth of the uplink that carries them. A 48-port gigabit switch with a single 10-gigabit uplink is 4.8 to 1. That is not automatically a problem, because ports are rarely all busy at once, but it tells you where congestion could show up first.

Enter your access ports (count and speed in Mbps) and your uplinks (count and speed in Mbps). You get the totals and the ratio, so you can compare designs, or check whether a new uplink or a second link would help.

How the math works

• Access capacity is the sum of port count times speed for the access ports.
• Uplink capacity is the sum of count times speed for the uplinks.
• The ratio is access capacity divided by uplink capacity.

A lower ratio is safer. What is acceptable depends on how busy your users are and what they do. Backups, video and storage traffic need more headroom than office browsing. Treat any ratio as a rule of thumb, and watch real utilization on the uplink over time.

Worked example

A switch has 48 ports at 1,000 Mbps, for 48,000 Mbps of access capacity. It has two uplinks at 10,000 Mbps each, for 20,000 Mbps. The ratio is 48,000 / 20,000 = 2.4 to 1. If you drop to a single uplink, the ratio rises to 4.8 to 1.