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.
About Load Balancer Capacity Calculator
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
Worked example
With the default values below, Load Balancer Capacity Calculator returns Concurrent Connections of 360,000. Change any input above and every figure here is recalculated in your browser.
Inputs used
- New connections per secondaccepts 1–5,000,000 cps
- 8,000 cps
- Average connection hold timeaccepts 0.01–86,400 s
- 45 s
- Load balancer nodes in the clusteraccepts 1–64 nodes
- 2 nodes
- Active/standby (only one node carries traffic)
- Yes
- Connection table limit per nodeaccepts 100–200,000,000 connections
- 500,000 connections
- Aggregate throughputaccepts 1–4,000,000 Mbps
- 4,000 Mbps
Results
- 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
Step by step
- 1Values used
- 2Load Balancer Capacity
- 3Concurrent Connections= 360,000
- 4Connections per Active Node= 360,000
- 5Connection Table Utilisation= 72.0
- 6Spare Table Entries= 140,000
- 7Bandwidth per Connection= 11.11 kbps
- 8Assessment= Sized with limited headroom
Assumptions and limits
- The result is derived only from the 6 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
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.