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Subscriber Capacity Calculator

Work out how many subscribers a cluster of core nodes supports, with redundancy reserved and headroom against today's load.

About Subscriber Capacity Calculator

Core nodes are licensed in sessions, not subscribers, and a modern handset holds more than one session at a time. Reserving a node for failover means the cluster's advertised capacity is deliberately lower than the sum of its parts. Sizing to the full cluster total is the classic mistake: the day one node fails, the remaining nodes reject sessions and the outage becomes a capacity incident rather than a redundancy event.

Formula

Subscriber Capacity

supported subscribers = (effective nodes × sessions per node) ÷ sessions per subscriber, where N+1 removes one node from the total.

effective nodes
Nodes available once the failover spare is set aside
sessions per subscriber
Concurrent PDN/PDU sessions the average subscriber holds

Worked example

With the default values below, Subscriber Capacity Calculator returns Subscribers Supported of 1,071,428. Change any input above and every figure here is recalculated in your browser.

Inputs used

Deployed nodesaccepts 1–200 nodes
4 nodes
Session capacity per nodeaccepts 1,000–100,000,000 sessions
500,000 sessions
Average sessions per subscriberaccepts 0.1–20 sessions
1.4 sessions
Reserve one node for failover (N+1)
Yes
Subscribers todayaccepts 0–200,000,000 subscribers
900,000 subscribers

Results

Subscribers Supported
1,071,428
Nodes Counted Toward Capacity
3
Headroom Above Today's Load
16.0%
Spare Subscriber Capacity
171,428

Step by step

  1. 1Values used
  2. 2Subscriber Capacity
  3. 3Subscribers Supported= 1,071,428
  4. 4Nodes Counted Toward Capacity= 3
  5. 5Headroom Above Today's Load= 16.0
  6. 6Spare Subscriber Capacity= 171,428

Assumptions and limits

  • The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 1 decimal place, 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 Subscriber Capacity calculated?

supported subscribers = (effective nodes × sessions per node) ÷ sessions per subscriber, where N+1 removes one node from the total. Core nodes are licensed in sessions, not subscribers, and a modern handset holds more than one session at a time. Reserving a node for failover means the cluster's advertised capacity is deliberately lower than the sum of its parts.

Why does Subscriber Capacity matter?

Sizing to the full cluster total is the classic mistake: the day one node fails, the remaining nodes reject sessions and the outage becomes a capacity incident rather than a redundancy event.

What values do I need to enter?

This calculator takes 5 inputs: Deployed nodes, Session capacity per node, Average sessions per subscriber, Reserve one node for failover (N+1), Subscribers today. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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