QoS Bandwidth Allocation Calculator
Split a link into voice, video, business and best-effort classes and check the 33% low-latency queue guideline.
About QoS Bandwidth Allocation Calculator
Each class gets a share of the link, and whatever is left over becomes the default best-effort queue. Voice and interactive video sit in the strict-priority queue, which industry guidance caps at roughly a third of the circuit so that starving the other classes is impossible. A policy that reserves more than the link can deliver, or puts more than a third in strict priority, will drop TCP flows in ways that look like a circuit fault rather than a config error.
Formula
QoS Bandwidth Allocation
class bandwidth = link rate × class share; best-effort = link rate × (100% − sum of all guaranteed shares).
- class share
- Percentage reserved for a traffic class by the scheduler
- LLQ
- Strict-priority queue, conventionally capped at a third of the link
Worked example
With the default values below, QoS Bandwidth Allocation Calculator returns Best-effort Bandwidth Left of 35.00. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Link rateaccepts 1–400,000 Mbps
- 100 Mbps
- Voice (EF) shareaccepts 0–100 %
- 10 %
- Interactive video (AF4) shareaccepts 0–100 %
- 20 %
- Business data (AF2/AF3) shareaccepts 0–100 %
- 30 %
- Scavenger (CS1) shareaccepts 0–100 %
- 5 %
Results
- Best-effort Bandwidth Left
- 35.00 Mbps
- Voice Guarantee
- 10.00 Mbps
- Video Guarantee
- 20.00 Mbps
- Business Data Guarantee
- 30.00 Mbps
- LLQ Guideline
- Within the 33% priority-queue guideline
- Policy Sums to 100% or Less
- Yes
Step by step
- 1Values used
- 2QoS Bandwidth Allocation
- 3Best-effort Bandwidth Left= 35.00 Mbps
- 4Voice Guarantee= 10.00 Mbps
- 5Video Guarantee= 20.00 Mbps
- 6Business Data Guarantee= 30.00 Mbps
- 7LLQ Guideline= Within the 33% priority-queue guideline
- 8Policy Sums to 100% or Less= Yes
Assumptions and limits
- The result is derived only from the 5 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 QoS Bandwidth Allocation calculated?
class bandwidth = link rate × class share; best-effort = link rate × (100% − sum of all guaranteed shares). Each class gets a share of the link, and whatever is left over becomes the default best-effort queue. Voice and interactive video sit in the strict-priority queue, which industry guidance caps at roughly a third of the circuit so that starving the other classes is impossible.
Why does QoS Bandwidth Allocation matter?
A policy that reserves more than the link can deliver, or puts more than a third in strict priority, will drop TCP flows in ways that look like a circuit fault rather than a config error.
What values do I need to enter?
This calculator takes 5 inputs: Link rate, Voice (EF) share, Interactive video (AF4) share, Business data (AF2/AF3) share, Scavenger (CS1) share. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.