How much does a 90% CDN cache hit ratio actually save?

A 90% hit ratio means only 10% of requests reach your origin — a 10× reduction in origin bandwidth and egress cost. This calculator models the full chain: requests × hit ratio × response size → origin bytes offloaded → dollar savings, so you can quantify the CDN decision before procurement instead of guessing.

What cache hit ratios should I expect for different content?

Ratios vary by content type — static assets like images, CSS, and JS typically hit 90%+ when caching headers are set correctly, while personalized or API content often sits much lower. The calculator includes benchmark ranges by content type so you can model realistic scenarios, plus the CloudFront free-tier nuance that changes the cost picture for small workloads.

How does edge caching reduce origin egress cost?

Each cache hit is served from the edge, so the origin never transmits those bytes and your origin egress bill shrinks proportionally. Bandwidth that would have crossed your cloud provider's paid egress is replaced by CDN delivery, which is usually billed at a lower rate or included in the CDN plan. The calculator separates offload savings from egress savings so both appear in the bottom line.

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🌐 CDN Edge Caching Bandwidth Offload

90% cache hit ratio means 10% of traffic still hits origin. At 10M requests/month with 50 KB average response, that is 50 GB of origin egress. At $0.09/GB, that is $4.50. Not scary. At 1B requests with 500 KB average, it is $45,000/month. Model it before you budget.

📦 Cache Configuration

Requests/month × average response size × cache-hit split. Total traffic, CDN-offloaded GB, residual origin traffic, and the dollar cost of what the cache does not absorb. Four numbers that anchor your CDN procurement conversation.

Total Requests (Millions/month)

CDN Cache Hit Ratio (%)

Avg Response Size (KB) API responses 1-10 KB · Images 50-500 KB · Video chunks 500+ KB

Origin Egress Rate ($/GB) AWS ~$0.09, CloudFront ~$0.085

CDN Cache Hit Ratio: 90% Caching = 10× Origin Cost Reduction

Content Delivery Networks (CDNs) operate on a simple but powerful premise: serve cached content from edge locations close to users, and only forward cache-miss requests to the origin server. Each percentage point of cache hit ratio directly reduces origin egress traffic, server load, and infrastructure cost. At a 90% cache hit ratio, only 10% of total traffic touches the origin — a 10× reduction in origin bandwidth demand and associated egress charges.

How This Calculator Models Cache Offload

The calculation is straightforward yet often overlooked during architecture planning:

Total Traffic (GB) = Total Requests × Average Response Size (KB) ÷ 1,000,000
CDN Offloaded (GB) = Total Traffic × Cache Hit Ratio
Origin Traffic (GB) = Total Traffic − CDN Offloaded
Origin Egress Cost ($) = Origin Traffic × Per-GB Egress Rate

Note: this calculator uses a flat per-GB rate for origin egress. For AWS tiered pricing (which applies volume discounts at scale), use the AWS Egress Cost Estimator for a more precise multi-band calculation.

Cache Hit Ratio Benchmarks by Content Type

Content Type	Typical Cache Hit Ratio	Key Factors
Static Assets (CSS, JS, images, fonts)	95–99%	Versioned URLs (fingerprinted filenames) enable indefinite caching. Immutable assets hit cache on every request after the first.
API Responses (semi-static data)	80–95%	Product catalogs, configuration, and reference data change infrequently. Set short TTLs (60–300s) with stale-while-revalidate to balance freshness and cache efficiency.
User-Generated Content (profiles, posts)	50–80%	Popular content is read frequently; tail content is rarely accessed. Cache warming and selective TTLs help optimize the Pareto distribution of requests.
Personalized / Authenticated Responses	0–20%	Per-user data is difficult to cache at the edge. Edge-side includes (ESI) or client-side personalization can separate cached templates from dynamic data.

CloudFront Free Tier: The Hidden Cost Advantage

AWS CloudFront includes a generous free tier: 1 TB of data transfer out per month, 10 million HTTP/HTTPS requests per month, and 2 million CloudFront Function invocations — all free, every month, indefinitely. For workloads under these limits, the CDN layer is effectively free, making the origin egress savings pure profit. Even beyond the free tier, CloudFront egress ($0.085/GB in the US) is often cheaper than direct S3/EC2 egress ($0.09/GB) for the first 10 TB — and the cache hit ratio multiplies those savings by reducing origin traffic.

Edge Caching Strategies for Maximum Offload

Maximizing cache hit ratio requires deliberate engineering. Use content-addressable URLs (hash in filename) for immutable assets to enable long-term caching. Apply Cache-Control: public, max-age=31536000, immutable for fingerprinted assets. For dynamic content, implement stale-while-revalidate (RFC 5861) to serve stale cached content while asynchronously refreshing — users never wait for origin latency. Configure origin shield (regional cache layers in CloudFront) to collapse multiple concurrent cache-miss requests into a single origin fetch, reducing origin load by an additional 60-80% for popular cacheable content.

Pricing Basis, Sources & Assumptions

Every rate on this page is a published vendor list price — no negotiated discounts, private pricing, or credit offsets. Totals are in USD and exclude tax. Rates were last checked against the sources below on 2026-09-23.

Pricing input	Basis used on this page
Region	US East (N. Virginia) for the AWS origin-egress default ($0.09/GB) and US/Canada for the CloudFront alternative ($0.085/GB). Both are published single-rate figures, not regional averages.
Currency	USD — on-demand list price, tax excluded
Last checked	2026-09-23 — The two origin rates offered as defaults — AWS direct egress at $0.09/GB and CloudFront at $0.085/GB — were re-checked on this date.

Modelling assumptions

Origin egress saved = total response bytes × cache hit ratio. The model treats the hit ratio as uniform across all objects.
The origin rate input is a single blended $/GB. Real origin bills are tiered, so the effective rate falls as volume grows — a flat rate is conservative at high volume.
What a cache hit saves is the origin leg only. The CDN-to-user leg is still billed, at the CDN's own rate, for every request.
Serving from cache is assumed to cost nothing beyond the CDN's base price — true for flat-rate CDNs, and approximately true for the free CloudFront tier.
Volumes are decimal: 1 TB = 1,000 GB.

What this model excludes

Request charges, which do not vary with the hit ratio and therefore do not shrink when caching improves.
Origin egress that CloudFront waives: delivery from S3 and from AWS load balancers to CloudFront is not billed as origin egress, so those origins show a smaller saving here than a non-AWS origin would.
Cache invalidation, purge fees, and increased storage for longer TTLs.
Compression and image-format conversion, which change the byte count before caching is even considered.

Sources

AWS (2026). "Amazon EC2 Data Transfer Pricing." Direct internet egress tiers — the $0.09/GB first tier used as the origin default. aws.amazon.com
AWS (2026). "Amazon CloudFront Pricing." The cheaper-at-scale alternative ($0.085/GB in North America) and the free tier. aws.amazon.com
Fastly (2026). "Fastly CDN Caching Concepts." How hit ratio translates into origin offload, and where the ratio is measured. developer.fastly.com

Vendor list prices change without notice — re-check the linked pages before committing spend. jslet takes no vendor sponsorship and carries no affiliate links; see about.