What Cache Hit Ratio Measures
Cache hit ratio is the percentage of requests that are served from cache rather than generated from scratch. A cache hit ratio of 90% means nine out of ten requests are served instantly from cached copies, while one in ten triggers a full rebuild. This single metric tells you whether your caching layer — whether page cache, object cache, or CDN — is actually doing its job.
What a healthy ratio looks like
For page caching, a healthy hit ratio is typically above 85-95%. For object caching (Redis or Memcached), ratios above 90% are normal for a properly configured setup. Ratios below 70% generally indicate a problem — either the cache is too small, invalidation is too aggressive, or traffic patterns prevent effective caching.
The “right” number depends on your site. A WooCommerce store with many logged-in shoppers will naturally have a lower page cache hit ratio than a blog, because logged-in users often bypass page caching. What matters is understanding what your baseline should be and spotting drops.
Why a low hit ratio matters
A low cache hit ratio means your server is doing unnecessary work. Every cache miss triggers a full PHP execution and database query cycle, which means higher server load, slower response times, and worse TTFB. On a shared hosting plan, a low hit ratio during traffic spikes can overwhelm the server entirely.
Common causes of low hit ratios
- Overly aggressive invalidation — cache invalidation rules that clear the entire cache on every post save or comment, forcing constant rebuilds.
- Too many cache variations — mobile vs desktop, logged-in vs logged-out, and cookie-based variations multiply the number of cached copies needed, reducing hit rates.
- Undersized object cache — if Redis or Memcached runs out of memory, it evicts entries that could have been served from cache.
- Low traffic volume — caching is less effective on low-traffic sites because entries expire before they are re-requested.
How to measure it
For object caching, the Redis CLI command INFO stats shows keyspace_hits and keyspace_misses. Query Monitor also displays cache hit statistics per page load. For page caching, some plugins (like LiteSpeed Cache) log hit/miss statistics, and CDN dashboards typically show cache hit ratios for edge-cached content.
Further Reading
- Prevent unnecessary network requests with the HTTP Cache (web.dev) — Explains HTTP caching mechanics that underpin browser and CDN cache behavior.