Practical guide
CloudFront cache hits: what they change in your cost estimate
understand CloudFront cache hit ratio and origin cost. Includes a worked example, calculator scope, and practical questions.
Updated · Sources checked
A cache hit still delivers content to the viewer
Improving a CDN cache hit ratio can reduce origin work, but it does not eliminate the bytes sent to the viewer. Keep viewer delivery and origin activity as separate usage models. Otherwise a higher cache hit ratio can produce an unrealistically low bandwidth forecast.
The CloudFront calculator estimates its supported delivery and request components. It does not calculate origin compute, database queries, or cache-dependent origin request costs.
Worked example: a higher request hit ratio
Assume ten million viewer requests during a month, each transferring a hypothetical average 50 KB. Viewer traffic is 500 billion bytes, or 500 decimal GB for this example.
At an 80% request hit ratio, a simplified model sends two million requests to origin. At 95%, that becomes 500,000 origin requests, a reduction of 1.5 million. In both scenarios, viewers still make ten million requests and receive the same 500 GB if response sizes are unchanged.
Enter the same viewer values into the delivery calculator for both cases. Estimate the avoided 1.5 million origin requests separately using the origin service’s pricing and workload behavior. A request hit ratio is not necessarily a byte hit ratio: misses may be systematically larger or smaller than hits.
Measure useful cacheability
Review which responses can be safely shared, how cache keys vary, and how often content changes. A cache configuration that ignores required personalization or serves stale critical data is not justified by an origin-cost reduction.
For the budget, segment large immutable assets from dynamic responses. Measure their request counts and average transferred sizes separately. This helps explain why an apparently strong overall hit ratio can coexist with substantial origin load.
CloudFront origin-transfer treatment depends on the source and pricing rules. Do not automatically charge each origin byte at a generic internet-egress rate as well as charging viewer delivery. The tool also excludes edge functions, invalidations, and flat-rate plans, which need separate evaluation where used.
Frequently asked questions
Does 95% cache hit ratio mean 95% off the CDN bill? No. The ratio primarily describes avoided origin fetches in this scenario, while viewer delivery continues.
Should hit ratio be entered into this calculator? No. Enter viewer delivery quantities. Keep a separate origin model to evaluate the impact of cache changes.
Calculate your scenario
Use the cloudfront cost calculator. Keep the displayed region, pricing date, billing units, and exclusions alongside your result. The arithmetic examples above illustrate usage or explicitly hypothetical rates; they are not AWS quotes.
Source
Billing structure checked against official AWS documentation on September 6, 2026.