Cache Hit Ratio Calculator
What a cache is actually buying — hit ratio, the effective average latency, and how much load it keeps off the origin.
Effective latency is the weighted average of hit and miss latency.
How the cache hit ratio calculator works
Effective latency is the weighted average of hit and miss latency. The non-obvious part is how sharply the returns diminish: going from 0 to 50% hit rate halves the origin load, but going from 90 to 95% halves it again — the same 5 percentage points near the top are worth ten times what they are worth in the middle.
That is why the last few per cent of hit rate are worth chasing on a hot cache and worthless on a cold one.
Formula: effective latency = h × hit + (1 − h) × miss
Worked examples
| Inputs | Effective latency (ms) | Note |
|---|---|---|
| 88% hit rate | 11.96 | 12 ms effective, 600 req/s to origin |
| A cold cache | 51.8 | origin load six times higher |
| Near-perfect | 2.83 | origin barely touched |
FAQFrequently asked questions
What is a good cache hit ratio?
For a CDN serving static assets, 90 to 98%. For an application cache it depends entirely on the access pattern — 70% can be excellent.
Why are the last few per cent worth so much?
Because origin load is the miss rate, not the hit rate. Going from 90 to 95% halves the misses; going from 40 to 45% removes only 8% of them.
Does a higher hit ratio always help?
Only if the misses were the problem. If the origin is comfortable and latency is already low, more cache buys nothing and costs memory.
What lowers a hit ratio?
Short TTLs, high cardinality in the cache key, and cold starts after a deploy. The cache key is usually the fixable one.
Is effective latency what users see?
It is the average. Users experience the distribution — the 12% who miss still wait the full 85 ms, and they are the ones who complain.
Where these figures come from
- IEC 80000-13 — Information science and technology (quantities and units) — the decimal (kB, MB) versus binary (KiB, MiB) prefixes used throughout
- RFC 4632 — Classless Inter-domain Routing (CIDR) — the address-plan arithmetic behind the subnet calculator
- RFC 1918 — Address Allocation for Private Internets — the private ranges the subnet calculator recognises
- NIST SP 800-63B — Digital Identity Guidelines, Authentication — length over composition rules; the basis of the password guidance here
- NIST SP 800-57 Part 1 — Recommendation for Key Management — key-strength comparisons used by the key-space calculator
- National Cyber Security Centre — password guidance — UK national guidance on password policy
Last checked: September 2026. Units follow the SI decimal convention (IEC 80000-13 defines the binary alternatives); network and security figures cite the defining standard.