CDN Origin Egress Calculator (Cache Misses)

Estimate how much traffic your origin actually serves. Start with edge bandwidth + edge requests, apply cache hit rate, and add a revalidation overhead to approximate cache fills and multi-POP refreshes.

Inputs

Edge bandwidth (GB / month)
From CDN analytics or billing exports.
Edge requests (per month)
Include cache hits + misses.
Cache hit rate (%)
Miss rate = 100% - hit rate.
Revalidation overhead (%)
Extra origin traffic from revalidations or multi-POP fills.
Scenario presets
This estimate is a planning model. Validate with CDN cache metrics and origin logs once live.

Results

Origin egress (GB / month)
630
Origin requests (per month)
47,250,000
Effective miss rate
15.75%
Origin share of edge GB
15.75%

How to get your inputs

  • Edge GB/month: use CDN analytics or billing exports.
  • Edge requests: use CDN request counts (all responses, hit + miss).
  • Hit rate: use cache metrics from your CDN dashboard.

Result interpretation

  • Origin egress is the input for your origin provider's $/GB pricing.
  • Origin requests can drive S3/ALB/API costs if your origin bills per request.

Common mistakes

  • Assuming origin egress is zero because the CDN exists.
  • Using cache hit rate from a short window (miss spikes during deploys or incidents).

Next steps

Origin egress cost S3 request cost Origin egress vs CDN bandwidth Guide: cache hit rate
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Example scenario

  • Edge 4,000 GB/month with 85% hit rate -> ~600 GB origin egress before revalidation overhead.
  • Edge 300M requests with 70% hit rate -> ~90M origin requests (plus overhead).

Included

  • Origin egress estimate from edge GB/month and cache hit rate.
  • Origin request estimate from edge requests/month and cache hit rate.
  • Optional revalidation overhead and peak hit-rate scenario.

Not included

  • Origin pricing ($/GB, $/request) - use Data Egress or S3 Request calculators.
  • CDN edge bandwidth and request fees - model separately.

How we calculate

  • Miss rate = 1 - hit rate.
  • Origin GB ~= edge GB x miss rate x (1 + revalidation overhead).
  • Origin requests ~= edge requests x miss rate x (1 + revalidation overhead).

FAQ

Why can origin egress be higher than edge bandwidth?
Cache revalidation, multi-POP fills, or low hit rate can create extra origin traffic beyond user delivery.
Should I use origin logs or CDN logs?
Use CDN cache metrics for hit rate, and origin logs/metrics for actual egress once live. This calculator is a planning model.
Does this include origin request pricing?
No. Use the S3 request or API request calculators with the origin request estimate if your origin charges per request.

Related tools

CDN cost calculator CDN bandwidth cost CDN request cost Origin egress cost Origin egress vs CDN bandwidth Guide: cache hit rate

Related guides

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Disclaimer

Educational use only. Not legal, financial, or professional advice. Results are estimates based on the inputs and assumptions shown on this page. Verify pricing and limits with your providers and documentation.

Last updated: 2026-01-30