Edge Cache Hit Rate Estimator
Calculate CDN edge cache hit rates with TTL analysis and optimization recommendations. Enter values for instant results with step-by-step formulas.
Formula
Hit Rate = Base Rate × Asset Coverage × TTL Factor + Cacheability Bonus
Base rate (85% industry average) is adjusted by cache size coverage of unique assets, TTL effectiveness (normalized to 1 hour), and percentage of cacheable content.
Worked Examples
Example 1: E-commerce Product Images
Problem:CDN serving 10M monthly requests for 50,000 product images. 80% cacheable, 2-hour TTL, 50GB edge cache, 150ms origin.
Solution:Cacheable: 10M × 80% = 8M requests Cache size: 50GB / 50KB avg = 1M assets (covers all) TTL factor: 120min/60 = 1.0 (optimal) Base hit rate: 85% × 1.0 × 1.0 = 85% With cacheability bonus: 85% + 8% = 93% Cache hits: 8M × 93% = 7.44M Cache misses: 560K Bypass: 2M Latency: (7.44M×20 + 2.56M×150)/10M = 53ms avg Origin load reduction: 74.4%
Result:93% hit rate | 53ms avg latency | 74% origin reduction
Example 2: News Site Articles
Problem:Media site: 5M daily requests, 10,000 articles, 60% cacheable (40% personalized), 15-min TTL for freshness, 5GB cache.
Solution:Cacheable: 5M × 60% = 3M requests Cache capacity: 5GB / 100KB = 50K articles (covers all) TTL factor: 15/60 = 0.25 (short TTL hurts) Base hit rate: 85% × 1.0 × 0.25 = 21.25% With cacheability: 21.25% + 6% = 27.25% This is LOW due to short TTL. Recommendation: Use stale-while-revalidate With SWR (simulated 4hr effective): 85% × 1.0 × 1.0 = 85%+ Trade-off: freshness vs performance
Result:27% hit rate (too low) | Implement SWR for 85%+ | Balance freshness
Example 3: SaaS Static Assets
Problem:SaaS app: 50M monthly requests, 2,000 JS/CSS/font files, 95% cacheable, 7-day TTL, 20GB cache, immutable versioning.
Solution:Cacheable: 50M × 95% = 47.5M requests Cache capacity: 20GB / 200KB = 100K files (50× coverage) TTL: 7 days >> 1 hour, factor = 1.0 Base hit rate: 85% × 1.0 × 1.0 = 85% With high cacheability: 85% + 9.5% = 94.5% With immutable versioning: +3% = 97.5% Cache hits: 47.5M × 97.5% = 46.3M Bypass: 2.5M Bandwidth saved: 46.3M × 200KB = 9.26TB/month Cost savings: ~$463/month at $0.00001/origin request
Result:97.5% hit rate | 9.26TB bandwidth saved | $463/mo savings
Frequently Asked Questions
What is cache hit rate?
Cache hit rate is the percentage of requests served from cache versus origin. A 90% hit rate means 90 of 100 requests are served from edge cache without contacting origin servers. Higher rates mean faster responses and lower origin load.
What is a good edge cache hit rate?
Industry benchmarks: 90%+ is excellent, 80-90% is good, 60-80% is fair, below 60% needs optimization. CDNs like Cloudflare report average hit rates of 85-95% for optimized sites. Static sites can achieve 99%+.
How does TTL affect cache hit rate?
Longer TTLs increase hit rates by keeping content cached longer. Short TTLs (minutes) suit dynamic content but reduce hits. Static assets should use long TTLs (days/weeks). Balance freshness vs performance based on content type.
What content should be cached at the edge?
Cache: static assets (JS, CSS, images, fonts), API responses that rarely change, HTML for static pages. Don't cache: personalized content, real-time data, authenticated responses, POST requests, content with Set-Cookie headers.
How do I improve cache hit rate?
Strategies: increase TTLs, normalize URLs (remove tracking params), use consistent cache keys, increase cache size, implement stale-while-revalidate, reduce asset variations, use cache-control headers properly, and pre-warm popular content.
What is cache eviction and why does it matter?
Cache eviction removes old content when cache is full. LRU (Least Recently Used) is common. Small caches with many assets cause frequent evictions, lowering hit rates. Size cache appropriately for your asset count.
How does edge caching reduce latency?
Edge servers are geographically closer to users (20-50ms) vs origin (100-300ms). Cache hits skip the origin round-trip entirely. A 90% hit rate with 200ms origin latency and 20ms edge latency yields ~38ms average.
What is origin shielding?
Origin shielding adds a middle-tier cache between edge and origin. Multiple edge POPs share one shield, reducing origin requests further. Useful for high-traffic sites with global distribution.
What is cache warming?
Cache warming pre-populates edge caches before traffic arrives. Useful after deployments, cache purges, or before traffic spikes. Tools like wget/curl can hit critical URLs across edge POPs.