CDN Cache Hit Ratio Calculator: Origin Bandwidth and Egress Savings
Estimate how much CDN caching reduces origin response traffic, average and peak origin bandwidth, and
origin egress cost. Compare your current cache hit ratio with a target scenario using measured delivered
data or a requests-times-response-size estimate.
Private by design: calculator values stay in your browser and are not submitted.
Traffic and cache inputs
Use response bytes delivered to viewers for the same period as the hit ratio.
Byte ratios are more reliable for bandwidth offload.
Use a byte share with a byte ratio or request share with a request ratio.
Byte-ratio model: the hit ratio is applied directly to response bytes. Prefer a provider byte-offload or cache-fill metric when available.
Estimated peak origin rate = period average × factor.
Leave blank to omit utilization.
Tip: press Ctrl/⌘ + Enter to recalculate.
Origin offload results
Current origin egress—
Estimated current peak origin bandwidth—
Origin egress avoided now—
Current origin egress savings—
Target scenario
Target origin egress—
Estimated target peak bandwidth—
Additional origin data avoided—
Additional egress savings—
Detailed comparison
Total CDN-delivered data—
No-cache origin egress cost—
Current origin egress cost—
Target origin egress cost—
Average origin bandwidth now—
Average origin bandwidth at target—
Origin traffic change vs current—
Current requests reaching origin—
Target requests reaching origin—
Estimated current peak capacity use—
Estimated target peak capacity use—
Enter valid inputs to calculate origin offload.
Worked example: 25 TB at an 80% hit ratio
With no uncacheable or bypass traffic, 25 TB delivered over 30 days at an 80% byte hit ratio leaves 5 TB of estimated origin response data:
25 TB × (1 − 0.80) = 5 TB. At 0.09 per GB, the estimated origin egress cost is 450,
while 20 TB served from cache avoids 1,800 of origin egress.
Raising the byte hit ratio to 90% lowers estimated origin response data to 2.5 TB and avoids another
2.5 TB, worth 225 at that same egress rate. The 30-day average origin rate falls from about 15.43 Mbps
to 7.72 Mbps; a 3× peak factor produces planning peaks of about 46.30 Mbps and 23.15 Mbps.
CDN cache offload formulas
Delivered bytes from requests:viewer requests × average response bytes
Origin egress cost:origin bytes ÷ 1,000,000,000 × price per GB
Origin egress savings:cache-served bytes ÷ 1,000,000,000 × price per GB
Data units and billing GB are decimal: 1 KB = 1,000 bytes, 1 GB = 1,000,000,000 bytes, and 1 TB = 1,000 GB.
A ratio of 100% produces zero estimated response-body traffic from misses, but real origins can still receive
revalidation, control, request-header, range-fill, purge, and logging traffic. Enter uncached or bypass response
traffic in the uncacheable share rather than assuming the hit ratio applies to it.
Request hit ratio versus byte hit ratio
CDN dashboards often define cache hit ratio as the percentage of cacheable requests served from cache.
That is useful for request load and latency, but it is not automatically the percentage of bytes offloaded.
A site can cache many small files successfully while missing a few large downloads, producing a high request
hit ratio and a lower byte offload ratio.
If you select Request hit ratio, this calculator uses a size-neutral approximation: hits and misses
are assumed to have the same average response size. For egress planning, prefer measured bytes from cache misses,
cache-fill bytes, or a provider byte hit ratio.
How to collect better CDN inputs
Input
Preferred source
Common pitfall
Delivered response data
CDN viewer-response bytes for the selected distribution and period
Mixing request bytes, uploads, or a different time window into the total
Byte offload
Origin/cache-fill response bytes compared with total delivered response bytes
Substituting request hit ratio when response sizes differ materially
Peak factor
Peak origin bits per second divided by average origin bits per second
Using a monthly average to size a burst-sensitive origin path
Egress price
Effective marginal origin-to-CDN rate after tiers, credits, and commitments
Adding CDN delivery pricing when the field is for origin egress only
Origin capacity
The smallest relevant sustained limit across server, NIC, load balancer, and upstream path
Treating provisioned bandwidth as guaranteed application throughput
Methodology and source notes
This is a deterministic planning model reviewed on July 28, 2026. Google Cloud documents cache hit ratio as
the share of requests served from cache and distinguishes cache egress from cache fill.
AWS similarly defines CloudFront cache hit rate by cacheable requests and notes that viewer bytes from misses
are an approximation of origin-to-edge bytes that can exclude refresh hits.
Apply the hit ratio to cache-eligible response bytes, then subtract cache-served bytes from total delivered bytes. With no bypass traffic, a 90% byte hit ratio attributes 10% of response bytes to misses at the origin.
What is the difference between request hit ratio and byte hit ratio?
Request hit ratio counts requests. Byte hit ratio weights each response by size. Use the latter for more accurate bandwidth and egress estimates.
Does the calculator include CDN charges?
No. It models only origin response-data egress at the price you enter. CDN delivery, cache-fill, request, invalidation, logging, tax, and other charges are outside the result.
Why can actual origin traffic be higher?
Revalidations, partial requests, range fills, multi-region cache warming, compression differences, request headers, errors, and provider-specific metric scopes can add traffic not represented by the simple response-byte model.
Can a target hit ratio be lower than the current ratio?
Yes. The calculator then shows additional data and savings as negative, which is useful for modeling a regression or a conservative scenario.
Are my inputs uploaded?
No. The calculations, copy output, and CSV creation run locally in your browser.
Limits and disclaimer
This calculator is an infrastructure planning aid, not a billing quote, performance guarantee, or capacity
certification. It assumes the selected hit ratio applies uniformly to delivered response bytes unless the
request-ratio approximation is selected. Validate production and financial decisions with CDN logs, origin
telemetry, provider billing exports, contract pricing, cache behavior, and load tests.
