Computer & IT
CDN Capacity Calculator
This calculator converts edge-node count and rated requests per second into raw, availability-adjusted, and safe delivery capacity. It buffers peak demand, estimates in-flight requests from service time, and rounds the edge capacity required for the planning case.
Raw rated throughput-
Availability-adjusted throughput-
Safe throughput at utilization ceiling-
Demand including growth buffer-
Safe capacity minus design demand-
Exact workers required-
Whole workers required-
Estimated concurrent in-flight work-
Peak demand utilization of safe capacity-
Current monthly infrastructure cost-
Required monthly infrastructure cost-
Decision view
CDN edge path and safe-capacity envelope
CDN edge path and safe-capacity envelopeRequests move from audience regions to edge delivery while raw, available, safe, and buffered design throughput remain distinct; cache-hit ratio and origin load are not inferred.
Exact scenario comparisonGrowth buffer (%) changes while all other entered assumptions remain constant.
| Growth buffer (%) | Raw rated throughput | Availability-adjusted throughput | Safe throughput at utilization ceiling | Demand including growth buffer | Safe capacity minus design demand | Exact workers required | Whole workers required | Estimated concurrent in-flight work | Peak demand utilization of safe capacity | Current monthly infrastructure cost | Required monthly infrastructure cost |
|---|
Period-by-period detail
CDN delivery growth-buffer capacity cases
How to use CDN Capacity Calculator
- Measure busy-period demand by region and content class rather than relying on a global daily average.
- Enter sustained edge throughput from representative object sizes, TLS behavior, and cache policies.
- Verify edge headroom and separately confirm that cache misses do not overload the origin.
Calculator guide
Understanding CDN Capacity Calculator
CDN capacity depends on safe edge throughput, request concurrency, cache effectiveness, regional imbalance, and the origin traffic that remains after caching.
Calculation method
How the calculation works
Compare buffered CDN requests with edge throughput to estimate safe capacity, concurrency, headroom, and cost. Multiply workers or edge channels by their rated throughput, apply availability and the utilization ceiling, and compare that safe capacity with buffered peak request demand.
Delivery topology
Follow a request from user to edge to origin
The topology view distinguishes edge-served traffic from the origin path and places buffered demand against safe delivery capacity.
Worked situations
Practical examples
- A globally healthy CDN can still saturate one region when demand is uneven.
- Longer service time raises concurrent work even if requests per second stay unchanged.
- A high cache-hit rate reduces origin load but does not remove edge egress limits.
Better inputs
Useful tips
- Track request rate, egress bandwidth, cache-hit ratio, origin fetches, and tail latency together.
- Reserve capacity for purge events, flash crowds, edge failures, and traffic steering.
- Test large-object and small-object workloads separately.
Before relying on the result
Limitations and common mistakes
- The model does not calculate cache-hit ratio, object-size distribution, egress bandwidth, origin shielding, or regional routing.
- Per-node throughput may not scale linearly because of shared network and storage limits.
- Entered monthly worker cost excludes transfer, request, security, and origin charges.
Reference
Key terms
- Edge capacity
- Request throughput available at CDN delivery locations.
- Origin load
- Traffic reaching the source infrastructure after cache behavior.
- Safe throughput
- Availability-adjusted capacity held below the utilization ceiling.
- Concurrency
- Approximate requests simultaneously in progress.
Important note
Calculated from the entered technical values using the displayed model. Validate topology, workloads, capacity, security, redundancy, and observed performance before implementation.
Frequently asked questions
Does this calculate cache-hit ratio?
No.
Why can latency increase before safe capacity is exceeded?
Burst queues, origin waits, or one hot region can degrade before aggregate saturation.
Is request capacity the same as bandwidth?
No; object size determines bytes transferred per request.
Can required nodes be fractional?
The exact need can, but deployable node count is rounded upward.