Flow Count Calculator

Estimate active flows and flow-cache utilisation from host count, flow rate and average flow duration.

About Flow Count Calculator

Flow arrivals and flow lifetime multiply to give the live population, exactly as with sessions. Comparing that against the exporter's cache size tells you whether flows age out naturally or get force-exported when the cache fills. An overflowing flow cache fragments long flows into many partial records, inflating collector storage and breaking any analysis that depends on complete flow duration or byte counts.

Formula

Flow Count

active flows = new flows per second × average flow duration; new flows/s = hosts × flows per minute ÷ 60.

new flows per second: Flow arrival rate
average flow duration: Mean flow lifetime in seconds
active flows: Entries live in the cache at any instant

Worked example

With the default values below, Flow Count Calculator returns Active Flows of 5,000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Active hostsminimum 1 hosts: 500 hosts
New flows per host per minuteminimum 0.1 flows/min: 30 flows/min
Average flow durationminimum 0.1 s: 20 s
Flow cache sizeminimum 1 entries: 65,536 entries

Results

Active Flows: 5,000
New Flows Per Second: 250.0 flows/s
Flow Records Per Hour: 900,000
Flow Cache Utilisation: 7.63%
Cache Overflow Risk: No — the cache holds the active set

Step by step

1Values used
2Flow Count
3Active Flows= 5,000
4New Flows Per Second= 250.0 flows/s
5Flow Records Per Hour= 900,000
6Flow Cache Utilisation= 7.63
7Cache Overflow Risk= No — the cache holds the active set

Assumptions and limits

The result is derived only from the 4 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 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 Flow Count calculated?

active flows = new flows per second × average flow duration; new flows/s = hosts × flows per minute ÷ 60. Flow arrivals and flow lifetime multiply to give the live population, exactly as with sessions. Comparing that against the exporter's cache size tells you whether flows age out naturally or get force-exported when the cache fills.

Why does Flow Count matter?

An overflowing flow cache fragments long flows into many partial records, inflating collector storage and breaking any analysis that depends on complete flow duration or byte counts.

What values do I need to enter?

This calculator takes 4 inputs: Active hosts, New flows per host per minute, Average flow duration, Flow cache size. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.