Flow Count Calculator
Estimate active flows and flow-cache utilisation from host count, flow rate and average flow duration.
Inputs
Active Flows
5,000
New Flows Per Second
250.0flows/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
Values used
Active hosts = 500 hosts; New flows per host per minute = 30 flows/min; Average flow duration = 20 s; Flow cache size = 65,536 entries
Flow Count
active flows = new flows per second × average flow duration; new flows/s = hosts × flows per minute ÷ 60.
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
How it works
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
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.
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