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IPS Throughput Calculator

Blend plaintext and TLS-inspected traffic to find the real throughput an IPS delivers, in both bits and packets per second.

About IPS Throughput Calculator

IPS capacity is not a single number: plaintext flows are inspected at the signature-set rate while decrypted flows run at the much lower TLS rate. Weighting the two by their share of traffic gives a blended figure, and dividing by the average frame size converts it into the packets per second the data plane must actually service. Most IPS deployments fail on the packet rate long before the bit rate, because small-packet traffic multiplies per-packet inspection cost while leaving the bandwidth graph looking comfortable.

Formula

IPS Throughput

effective = (plaintext share × rated × signature derate) + (TLS share × rated × TLS derate); pps = effective bits ÷ (packet size × 8).

signature derate
Fraction of rated throughput left with the chosen signature set
TLS derate
Fraction of rated throughput left when decrypting

Worked example

With the default values below, IPS Throughput Calculator returns Blended Inspected Throughput of 7.40. Change any input above and every figure here is recalculated in your browser.

Inputs used

Rated L4 throughputaccepts 0.1–2,000 Gbps
20 Gbps
Signature setone of Connectivity / L4 only (100%), Recommended baseline set (50%), Balanced signature set (45%), Security-first, all signatures (35%)
Balanced signature set (45%)
Share of traffic decrypted for inspectionaccepts 0–100 %
40 %
Throughput remaining under TLS inspectionaccepts 1–100 %
25 %
Peak offered loadaccepts 0–2,000 Gbps
6 Gbps
Average packet sizeaccepts 64–9,000 bytes
700 bytes

Results

Blended Inspected Throughput
7.40 Gbps
Utilisation at Peak Load
81.1%
Headroom
1.40 Gbps
Inspected Packet Rate
1,321,429 pps
Sizing Verdict
Tight — under 20% headroom

Step by step

  1. 1Values used
  2. 2IPS Throughput
  3. 3Blended Inspected Throughput= 7.40 Gbps
  4. 4Utilisation at Peak Load= 81.1
  5. 5Headroom= 1.40 Gbps
  6. 6Inspected Packet Rate= 1,321,429 pps
  7. 7Sizing Verdict= Tight — under 20% 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 IPS Throughput calculated?

effective = (plaintext share × rated × signature derate) + (TLS share × rated × TLS derate); pps = effective bits ÷ (packet size × 8). IPS capacity is not a single number: plaintext flows are inspected at the signature-set rate while decrypted flows run at the much lower TLS rate. Weighting the two by their share of traffic gives a blended figure, and dividing by the average frame size converts it into the packets per second the data plane must actually service.

Why does IPS Throughput matter?

Most IPS deployments fail on the packet rate long before the bit rate, because small-packet traffic multiplies per-packet inspection cost while leaving the bandwidth graph looking comfortable.

What values do I need to enter?

This calculator takes 6 inputs: Rated L4 throughput, Signature set, Share of traffic decrypted for inspection, Throughput remaining under TLS inspection, Peak offered load, Average packet 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.

What happens when an IPS runs out of capacity?

It depends on the configured failure mode. Fail-open preserves availability by forwarding uninspected traffic, which is a silent security gap; fail-closed preserves security by dropping, which is an outage. Sizing with real headroom is how you avoid ever making that choice under pressure.

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