DDoS Capacity Calculator
Compare scrubbing capacity against a modelled attack volume to see whether your DDoS headroom ratio actually holds.
Inputs
Plan against the largest attack seen in your sector, not the average.
Scrubbing Headroom Ratio
3.00×
Scrubbing Capacity Consumed
33.3%
Spare Scrubbing Capacity
800.0Gbps
On-Premises Survival Ratio
0.25×
Attack-to-Legitimate Ratio
50.0×
Readiness Verdict
Strong — at least 3x scrubbing headroom
Step by step
Values used
Scrubbing capacity available = 1,200 Gbps; Modelled attack volume = 400 Gbps; On-premises internet link capacity = 100 Gbps; Normal legitimate traffic = 8 Gbps
DDoS Capacity
headroom ratio = scrubbing capacity ÷ attack volume; on-premises survival ratio = link capacity ÷ attack volume.
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
How it works
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
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.