Load Balancer Capacity Calculator
Size a load balancer pair from connection arrival rate and hold time, and check the state table against the per-node limit.
Inputs
Concurrent Connections
360,000
Connections per Active Node
360,000
Connection Table Utilisation
72.0%
Spare Table Entries
140,000
Bandwidth per Connection
11.11kbps
Assessment
Sized with limited headroom
Step by step
Values used
New connections per second = 8,000 cps; Average connection hold time = 45 s; Load balancer nodes in the cluster = 2 nodes; Active/standby (only one node carries traffic) = Yes; Connection table limit per node = 500,000 connections; Aggregate throughput = 4,000 Mbps
Load Balancer Capacity
concurrent connections = new connections per second × average hold time (Erlang-style concurrency); utilisation = concurrent ÷ per-node table limit.
Concurrent Connections
= 360,000
Connections per Active Node
= 360,000
Connection Table Utilisation
= 72.0
Spare Table Entries
= 140,000
Bandwidth per Connection
= 11.11 kbps
Assessment
= Sized with limited headroom
How it works
A connection table holds one entry per live flow, and the number of live flows is the arrival rate multiplied by how long each one lasts. In active/standby only one node carries the load, so the surviving node must fit the entire table on its own. Load balancers are almost never limited by bandwidth — they run out of connection-table entries first, and an active/active cluster sized at 80% cannot survive losing a node.
Formula
Load Balancer Capacity
concurrent connections = new connections per second × average hold time (Erlang-style concurrency); utilisation = concurrent ÷ per-node table limit.
- holdTime
- How long a connection occupies a table entry, including idle timeout
- activeNodes
- 1 in active/standby, the full cluster in active/active
Frequently Asked Questions
How is Load Balancer Capacity calculated?
concurrent connections = new connections per second × average hold time (Erlang-style concurrency); utilisation = concurrent ÷ per-node table limit. A connection table holds one entry per live flow, and the number of live flows is the arrival rate multiplied by how long each one lasts. In active/standby only one node carries the load, so the surviving node must fit the entire table on its own.
Why does Load Balancer Capacity matter?
Load balancers are almost never limited by bandwidth — they run out of connection-table entries first, and an active/active cluster sized at 80% cannot survive losing a node.
What values do I need to enter?
This calculator takes 6 inputs: New connections per second, Average connection hold time, Load balancer nodes in the cluster, Active/standby (only one node carries traffic), Connection table limit per node, Aggregate throughput. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.