CDN Cache Hit Ratio Impact Estimator
At 80% cache hit ratio, your origin still fields 1 in 5 requests. CloudFront bills every single one. Going from 80% to 95% hit ratio doubles your offload — and halves your origin costs. Quantify the dollar impact before you negotiate the CDN contract.
📐 Traffic & Cache Profile
Set your sustained req/s, object size, and cache hit ratio. The engine splits traffic into cache-hit and cache-miss fractions, then prices each against CloudFront, Cloudflare, Fastly, BunnyCDN, and KeyCDN — with origin-only as the baseline comparison.
📋 CDN Provider Pricing Reference (as of 2026)
Published list pricing for major CDN providers. Enterprise agreements, reserved capacity, and volume commitments may reduce actual costs significantly.
| Provider / Plan | Bandwidth ($/GB) | Requests ($/M) | Base Fee/mo | Free Tier / Notes |
|---|---|---|---|---|
| CF CloudFront (US/CA) | $0.085 | $0.0075 | $0 | 1 TB free egress × 12 mo |
| CF CloudFront (Reserved 10TB+) | $0.060 | $0.0060 | $0 | 12-month commitment |
| FLR Cloudflare CDN (Free) | $0.00 | $0.00 | $0 | Unmetered DDoS, shared SSL |
| FLR Cloudflare Pro | $0.00 | $0.00 | $20 | Image optimization, WAF rules |
| FLR Cloudflare Business | $0.00 | $0.00 | $200 | 100% uptime SLA, PCI compliance |
| FSL Fastly (Pay-as-you-go) | $0.12 | $0.0075 | $0 | First $50 credit, instant purge |
| FSL Fastly (Enterprise) | $0.08 | $0.0050 | $500+ | Custom contract, dedicated POPs |
| BNY BunnyCDN (Standard) | $0.01 | — | $0 | Pay-per-GB, no request fees |
| BNY BunnyCDN (Volume ≥500TB) | $0.005 | — | $0 | Tiered volume discounts |
| KEY KeyCDN (Pay-as-you-go) | $0.04 | — | $0 | Pay-per-GB, 34+ POPs |
| ORG Origin-Only (No CDN) | $0.09 | — | $0 | All traffic hits origin; full egress |
CDN Cache Hit Ratio Economics: Why Every 1% Matters at Scale
Cache Hit Ratio (CHR) is the percentage of requests served directly from CDN edge nodes without contacting the origin server. At high traffic volumes, each percentage point of cache efficiency represents significant cost savings. A service handling 5,000 requests per second with 100 KB average object size and a 95% CHR offloads roughly 12.3 PB/year of traffic from origin — at $0.09/GB origin egress, that's over $1.1 million/year in avoided origin bandwidth costs.
How This Estimator Works
The engine computes monthly request volume from your sustained req/s rate (req/s × 86,400 × 30.4375 mean days/month), then splits it into cache-hit and cache-miss fractions based on your target hit ratio. Cache hits incur CDN bandwidth pricing; cache misses incur both CDN request/bandwidth costs (for the miss-forward) and origin egress costs (for the fetch). The total cost is compared against an all-origin baseline to compute net savings.
| Component | Formula | Charged By |
|---|---|---|
| Cache Hit Requests | Monthly Requests × Hit Ratio | CDN bandwidth only (edge → client) |
| Cache Miss Requests | Monthly Requests × (1 − Hit Ratio) | CDN request fee + CDN bandwidth + Origin egress (fetch) |
| Origin Egress Savings | Cache Hits × Object Size × Origin $/GB | Avoided origin bandwidth cost |
| Total CDN Cost | CDN Bandwidth + CDN Request Fees + Base Fee | CDN provider invoice |
| Net Savings | Origin-Only Cost − (CDN Cost + Residual Origin Cost) | Bottom-line infrastructure reduction |
Cache Hit Ratio Tiers: What's Achievable?
| Content Type | Typical CHR | TTL Strategy | Key Optimization |
|---|---|---|---|
| Static assets (JS, CSS, images, fonts) | 95–99% | Long TTL (7–365 days), content-hash filenames | Immutable URLs with cache busting |
| Product images (e-commerce) | 80–92% | Medium TTL (1–7 days), stale-while-revalidate | Image CDN with resizing at edge |
| CDN-cached API responses | 55–75% | Short TTL (1–60 min), surrogate keys for purge | Cache-Control: s-maxage with fast purge |
| Video segments (HLS/DASH) | 96–99.5% | Long TTL, multi-tier (L1/L2 CDN) | Pre-warming for popular content |
| Dynamic / personalized HTML | 0–15% | No cache or edge-side includes | Edge compute (Cloudflare Workers, Lambda@Edge) |
| User-generated content | 30–60% | Short TTL, popularity-based eviction | Tiered caching (regional → origin shield) |
Beyond Cost: Latency and Availability Benefits
Cache hit ratio doesn't just save money — it directly improves user experience and system resilience:
- Latency reduction: A cache hit served from a nearby edge POP (1–10ms) instead of a cross-continent origin fetch (50–300ms) delivers 10–100× faster response times.
- Origin load shedding: A 95% CHR means the origin handles only 5% of total traffic — allowing smaller, cheaper origin infrastructure (fewer servers, lower DB load).
- DDoS absorption: CDN edge nodes absorb volumetric attacks at the network edge. Even during an attack, cacheable content continues serving without origin impact.
- Availability improvement: If the origin fails, cached content remains available (graceful degradation). A stale-while-revalidate directive extends this window to hours.
- Carbon reduction: Edge serving eliminates long-haul data transfers. Each TB served from edge vs. origin reduces CO₂ emissions by an estimated 3–5 kg.
Cache Invalidation: The Hidden Cost Driver
High cache hit ratios require effective invalidation — purging stale content when it changes. Different CDNs offer different invalidation models:
| Provider | Invalidation Method | Speed | Cost |
|---|---|---|---|
| CloudFront | CreateInvalidation (path/wildcard) | ~60–300s globally | Free (first 1,000 paths/month) |
| Cloudflare | Purge by URL / prefix / tag / hostname | Instant (<1s globally) | Free (unlimited) |
| Fastly | Surrogate keys + instant purge API | ~150ms globally | Included in per-request pricing |
| BunnyCDN | Purge by URL / all | ~5–30s globally | Free (unlimited zones) |
| KeyCDN | Purge by URL / tag / all | Instant (<1s globally) | Free (unlimited) |
Fastly's surrogate-key model is uniquely powerful for API caching: tag each response with its resource type and ID (e.g., product-1234, category-electronics), then purge by tag — one API call can invalidate hundreds of related URLs simultaneously. This enables high CHR with shorter effective TTLs because invalidation is cheap and instant.
The Origin Shield / Tiered Caching Multiplier
Most major CDNs offer an "origin shield" or "tiered caching" feature — a regional intermediate cache layer that sits between edge POPs and your origin. When an edge POP has a cache miss, it fetches from the regional shield rather than directly from origin:
| Scenario | Edge CHR | Effective Origin Hit | Origin Load Reduction |
|---|---|---|---|
| No shield, 90% edge CHR | 90% | 10% | 10× reduction (90% offloaded) |
| With shield, 90% edge CHR + 80% shield CHR | 90% | 2% | 50× reduction (98% offloaded) |
| With shield, 95% edge CHR + 90% shield CHR | 95% | 0.5% | 200× reduction (99.5% offloaded) |
This estimator models single-tier caching (edge → origin). If your architecture includes an origin shield, the effective origin offload is significantly higher than the edge CHR alone suggests. The formula is: Effective Origin Load = (1 − Edge_CHR) × (1 − Shield_CHR). A 95% edge CHR with 90% shield CHR means origin sees only 0.5% of total traffic.
Cache Hit Ratio vs. Byte Hit Ratio
CDNs report two distinct metrics: Request Hit Ratio (percentage of requests served from cache) and Byte Hit Ratio (percentage of bytes served from cache). These diverge significantly when object sizes vary. A site serving mostly small API responses (cached at 70% request ratio) but a few large video files (also cached) may have a 95% byte hit ratio while request hit ratio sits at 80%. This calculator uses request-based hit ratio because CDN pricing is typically per-request or per-GB — both dimensions directly map to cost.
📎 Embed This Calculator
Embed the CDN cache hit ratio impact calculator on your team wiki, architecture doc, or CDN evaluation page. No API key. No tracking. 100% client-side.
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