Uplink Oversubscription Calculator

The ratio between a switch's access-port bandwidth and the uplinks that carry it, with the peak load and the uplink count a target ratio needs.

Access ports

Access port speed

Peak access utilization

Uplink ports

Uplink port speed

Target ratio

How many access ports the switch presents downstream. Count every port that can carry load.

Line rate of one access port. Mixed speeds are not averaged: calculate each speed group separately.

The share of the access capacity you expect at the busiest moment, as a percentage of line rate. Real access traffic is bursty and far below line rate on average.

Uplink ports that are active and carrying traffic. Standby or blocked members of a bundle contribute no usable bandwidth.

Line rate of one uplink port.

The oversubscription ratio this boundary should stay within, written as X:1. Access edges are commonly allowed 20:1; aggregation and core links usually sit at 4:1 or below.

Oversubscription is the combined line rate of the access ports divided by the combined line rate of the active uplinks, written X:1. Two uplinks of 10 Gbps behind 48 ports of 1 Gbps is 48 ÷ 20, or 2.4:1, which means all access ports together cannot send at full line rate at once. A ratio above 1 is normal and intended at the access edge because endpoints rarely transmit simultaneously; the peak-utilization figure turns that design ratio into the load the uplinks actually carry, and the headroom is what is left at that load. The ratio says nothing about measured throughput, queueing, latency, per-flow hashing or traffic that stays on the same switch, and a bundle member that is standby or blocked does not add capacity. Values are refused outside 1 to 4096 access ports, 1 to 256 uplink ports, 1% to 100% peak utilization and a 1:1 to 100:1 target, and decimal commas are accepted. This is a planning estimate for a single boundary, it is not a design certification, and it runs entirely in your browser with no storage, uploads or network access.