--- title: What is a Cache Hit Ratio? description: A CDN should have a high cache hit ratio. Learn about the difference between a cache hit and a cache miss, and how to calculate a cache hit ratio. image: https://www.cloudflare.com/preview.png --- ## What is a cache hit ratio? A cache hit ratio is calculated by dividing the number of cache hits by the total number of cache hits and misses, and it measures how effective a cache is at fulfilling requests for content. ###### Learning objectives After reading this article you will be able to: * Understand the difference between a cache hit and a cache miss * Learn how to calculate cache hit ratio * Understand the importance of cache hit ratio for CDNs Related content On this page ## What is a cache hit ratio? Cache hit ratio is a measurement of how many content requests a cache is able to fill successfully, compared to how many requests it receives. A [content delivery network (CDN)](/learning/cdn/what-is-a-cdn/) provides a type of [cache](/learning/cdn/what-is-caching/), and a high-performing CDN will have a high cache hit ratio. The formula for calculating a cache hit ratio is as follows: ![Cache hit ratio equation](https://images.ctfassets.net/slt3lc6tev37/9tqnmxxbqjmGcBQPvMgJN/a804f98a247f09bd21e42c398c507e96/cache-hit-ratio.svg) Cache hit ratio equation For example, if a CDN has 39 cache hits and 2 cache misses over a given timeframe, then the cache hit ratio is equal to 39 divided by 41, or 0.951\. The cache hit ratio can also be expressed as a percentage by multiplying this result by 100\. As a percentage, this would be a cache hit ratio of 95.1%. Cache hit ratio is a metric that applies to any cache; it's not just for measuring [CDN performance](/learning/cdn/performance/). However, it is an especially important benchmark for CDNs. Most CDN services will provide customers with this metric within their user interface or dashboard. ## What is a cache hit? A "cache hit" occurs when a file is requested from a cache and the cache is able to fulfill that request. For instance, if a user visits a webpage that's supposed to display a picture of a cat playing a piano, the browser may send a request to the webpage's CDN for this picture. If the CDN has a copy of the picture in its storage, then the request results in a cache hit, and the picture is sent to the browser. ## What is a cache miss? A cache miss is when the cache does not contain the requested content. If a copy of the cat-playing-piano picture is not currently in the CDN cache, this request results in a cache miss, and the request is passed along to the [origin server](/learning/cdn/glossary/origin-server/) for the original picture. The CDN server will cache the photo once the origin server responds, so that additional requests for it will result in a cache hit. ## What is a good CDN cache hit ratio for most websites? A typical website that's mostly made up of static content could easily have a cache hit ratio in the 95-99% range. However, getting this metric as high as possible isn't the only goal of a CDN. Additionally, a website with lots of dynamic content may have a much lower cache hit ratio (although caching dynamic content is becoming possible). ## Does a high cache hit ratio always mean a CDN is effective? Cache hit ratio is not the last word in CDN performance; other factors are extremely important in assessing a CDN's effectiveness as well. For instance, [where the content is served from](/learning/cdn/performance/) is also important. Ideally, a CDN will serve content from the CDN server closest to the end user. If this doesn't occur, the CDN's performance will not be optimal. The [Cloudflare CDN](https://www.cloudflare.com/application-services/products/cdn/) is built to serve any content from any of our 335+ locations around the world. Any content that is cached in one data center) can be served from every other data center as well. [Caching](/learning/cdn/what-is-caching/) is an important part of what a CDN does, but its main purpose is to make web properties faster and more reliable in general. A variety of [performance metrics](/learning/performance/test-the-speed-of-a-website/) help measure how much a CDN has helped to speed up a web app or website. ```json {"@context":"https://schema.org","@type":"Organization","name":"Cloudflare","url":"https://www.cloudflare.com","logo":"https://www.cloudflare.com/logo.svg","sameAs":["https://github.com/cloudflare","https://www.linkedin.com/company/cloudflare","https://x.com/cloudflare"]} {"@context":"https://schema.org","@type":"WebSite","name":"Cloudflare","url":"https://www.cloudflare.com","inLanguage":"en","potentialAction":{"@type":"SearchAction","target":"https://www.cloudflare.com/search?q={search_term_string}","query-input":"required name=search_term_string"}} {"@context":"https://schema.org","@type":"WebPage","name":"What is a Cache Hit Ratio?","description":"A CDN should have a high cache hit ratio. 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