THE NUMBERS, EXPLAINED
How to use this calculator.
Every request pays the cache lookup charge; only misses pay the origin charge. Supplied flat rates exclude storage, bandwidth, tax, free tiers and minimum charges. Expected miss counts may be fractional.
Start with your inputs
Enter requests, cache hit rate (%), origin cost per 1,000 requests (£), cache lookup cost per 1,000 requests (£). Keep amounts in the units shown on each field. The example is a starting point, not a recommended value.
| Input | Example value |
|---|---|
| Requests | 1000000 |
| Cache hit rate (%) | 90 |
| Origin cost per 1,000 requests (£) | 2 |
| Cache lookup cost per 1,000 requests (£) | 0.1 |
A worked example
With the example inputs above, expected origin requests is 100,000. Change the inputs to explore your own scenario.
| Result | Example answer |
|---|---|
| Expected origin requests | 100,000 |
| Origin cost (£) | 200 |
| Cache cost (£) | 100 |
| Combined cost (£) | 300 |
| Saving versus origin only (£) | 1,700 |
How this is calculated
Expected origin requests
Requests × (1−hit rate/100).
Origin cost (£)
Expected misses × origin rate ÷ 1,000.
Cache cost (£)
All requests × cache rate ÷ 1,000.
Combined cost (£)
Add origin and cache costs.
Saving versus origin only (£)
Origin-only request cost minus combined cost.
Symbols and units
- a
- Requests
- b
- Cache hit rate (%)
- c
- Origin cost per 1,000 requests (£)
- d
- Cache lookup cost per 1,000 requests (£)
Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.
Assumptions and limits
Every request pays the cache lookup charge; only misses pay the origin charge. Supplied flat rates exclude storage, bandwidth, tax, free tiers and minimum charges. Expected miss counts may be fractional.
Calculations use the values you enter. Blank or invalid inputs show an error instead of silently substituting zero. Results are displayed to useful precision; calculations retain the underlying numeric precision.
Questions about this tool
What does the result tell me?
Expected origin requests; Origin cost (£); Cache cost (£); Combined cost (£); Saving versus origin only (£). The result applies to the method and inputs described above. Check the units and assumptions before using it in a decision.
Why might another calculator differ?
Differences in units, rounding, timing or model definitions can produce different answers. Compare the input definitions and the method, rather than only the final number. For this tool: Every request pays the cache lookup charge; only misses pay the origin charge. Supplied flat rates exclude storage, bandwidth, tax, free tiers and minimum charges. Expected miss counts may be fractional.
Are my inputs stored or sent to AI?
Calculations on this page happen in your browser. The separate AI question finder sends its submitted conversation to OpenAI; these calculator fields are not sent. Favourites and recent tool names are stored locally. A shared link contains the inputs you choose to include.
Further reading
OpenStax: percentages and proportions ↗
Background reading; this does not imply endorsement or independent review of SumFizz.
Review status
Software example and browser checks are recorded in our quality report. No external expert review is claimed. Created with coding assistance; calculations run as ordinary browser code.
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