CDN Cache Hit Savings Calculator
See how a CDN cache hit ratio cuts origin bandwidth and cost: the higher the hit rate, the less traffic reaches your server and the smaller your egress bill.
How it works
Origin GB = total × (1 − hit%) · With-CDN = origin GB × origin $/GB + total × CDN $/GB · Saved = origin-only − with-CDN
A CDN caches your content at edge locations, so a request that hits the cache never touches your origin server. The cache hit ratio is the share of traffic served from the edge; only the misses — the remaining fraction — reach origin and incur your expensive origin egress. The CDN charges its own, usually cheaper, per-GB rate on everything it delivers. Savings grow steeply with the hit ratio, which is why cache-friendly headers, long TTLs on static assets and high cacheability are worth the tuning effort.
Worked example
Delivering 2,000 GB a month at a 90% hit ratio means only 200 GB reaches origin. Serving all 2,000 GB from origin at $0.09/GB would cost $180; with the CDN you pay 200 × $0.09 = $18 origin plus 2,000 × $0.02 = $40 CDN = $58, saving $122 a month.
Frequently asked questions
What is a good cache hit ratio?
For mostly static sites, 90%+ is achievable and 95–99% is common with good caching headers. Dynamic, personalised or frequently changing content caches poorly, dragging the ratio down. Measure your real ratio in the CDN dashboard rather than assuming — a low ratio often points to missing or too-short cache-control headers.
Why can a CDN sometimes cost more?
If your hit ratio is low and the CDN’s per-GB rate is not much below your origin’s, you pay the CDN on all traffic plus origin on the misses, which can exceed origin-only cost. CDNs pay off through a high hit ratio and a real per-GB gap; the main wins are also latency and origin load, not cost alone.
Does the CDN charge for cache misses too?
Most CDNs bill their per-GB delivery rate on every byte they serve to visitors, hit or miss, and you separately pay origin egress on the misses that they fetch from your server. This calculator applies the CDN rate to all delivered traffic and the origin rate only to the miss fraction.
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This calculator is for educational purposes. Double-check important results before acting on them.