DDoS Capacity Calculator
Compare scrubbing capacity against a modelled attack volume to see whether your DDoS headroom ratio actually holds.
About DDoS Capacity Calculator
Volumetric defence is a simple ratio problem: divide the scrubbing capacity you can actually invoke by the attack volume you plan against. A ratio below 1 means the attack saturates the scrubber; below 1.5 means you have no margin for the attack growing mid-event, which is exactly what attackers do when the first wave fails. Any attack larger than your internet link saturates it before a single on-premises appliance sees a packet, which is why the survival ratio, not the appliance datasheet, decides whether you stay online.
Formula
DDoS Capacity
headroom ratio = scrubbing capacity ÷ attack volume; on-premises survival ratio = link capacity ÷ attack volume.
- scrubbing capacity
- Aggregate clean-pipe capacity of your provider or appliance
- attack volume
- Peak bits per second of the modelled attack
Worked example
With the default values below, DDoS Capacity Calculator returns Scrubbing Headroom Ratio of 3.00. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Scrubbing capacity availableaccepts 1–100,000 Gbps
- 1,200 Gbps
- Modelled attack volumeaccepts 0.1–100,000 Gbps
- 400 Gbps
- On-premises internet link capacityaccepts 0.1–10,000 Gbps
- 100 Gbps
- Normal legitimate trafficaccepts 0.01–10,000 Gbps
- 8 Gbps
Results
- Scrubbing Headroom Ratio
- 3.00 ×
- Scrubbing Capacity Consumed
- 33.3%
- Spare Scrubbing Capacity
- 800.0 Gbps
- On-Premises Survival Ratio
- 0.25 ×
- Attack-to-Legitimate Ratio
- 50.0 ×
- Readiness Verdict
- Strong — at least 3x scrubbing headroom
Step by step
- 1Values used
- 2DDoS Capacity
- 3Scrubbing Headroom Ratio= 3.00 ×
- 4Scrubbing Capacity Consumed= 33.3
- 5Spare Scrubbing Capacity= 800.0 Gbps
- 6On-Premises Survival Ratio= 0.25 ×
- 7Attack-to-Legitimate Ratio= 50.0 ×
- 8Readiness Verdict= Strong — at least 3x scrubbing headroom
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 DDoS Capacity calculated?
headroom ratio = scrubbing capacity ÷ attack volume; on-premises survival ratio = link capacity ÷ attack volume. Volumetric defence is a simple ratio problem: divide the scrubbing capacity you can actually invoke by the attack volume you plan against. A ratio below 1 means the attack saturates the scrubber; below 1.5 means you have no margin for the attack growing mid-event, which is exactly what attackers do when the first wave fails.
Why does DDoS Capacity matter?
Any attack larger than your internet link saturates it before a single on-premises appliance sees a packet, which is why the survival ratio, not the appliance datasheet, decides whether you stay online.
What values do I need to enter?
This calculator takes 4 inputs: Scrubbing capacity available, Modelled attack volume, On-premises internet link capacity, Normal legitimate traffic. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
Why aim for 3× headroom rather than 1×?
Scrubbing capacity is shared across every customer of the provider, attacks routinely double when the first attempt is mitigated, and reflection vectors can add hundreds of gigabits in seconds. A 3× ratio absorbs a simultaneous second target and an attack that escalates without renegotiating capacity mid-incident.