THE NUMBERS, EXPLAINED
How to use this calculator.
Each uncached visit downloads every listed font weight. Cached visits transfer no font bytes. Both scenarios use the same cache-hit assumption. Confirm that the subset retains every required glyph; headers and revalidation are excluded.
Start with your inputs
Enter original font bytes by weight, subset font bytes by weight, visits, visits with all fonts cached (%). Keep amounts in the units shown on each field. The example is a starting point, not a recommended value.
| Input | Example value |
|---|---|
| Original font bytes by weight | 10000,20000 |
| Subset font bytes by weight | 4000,5000 |
| Visits | 1000 |
| Visits with all fonts cached (%) | 20 |
A worked example
With the example inputs above, original transfer (bytes) is 24,000,000. Change the inputs to explore your own scenario.
| Result | Example answer |
|---|---|
| Original transfer (bytes) | 24,000,000 |
| Subset transfer (bytes) | 7,200,000 |
| Transfer saved (bytes) | 16,800,000 |
| Reduction (%) | 70 |
How this is calculated
Original transfer (bytes)
Sum original sizes × visits × (1−cached percentage/100).
Subset transfer (bytes)
Sum subset sizes × uncached visits.
Transfer saved (bytes)
Original transfer minus subset transfer.
Reduction (%)
Byte reduction per uncached visit divided by original bytes × 100.
Symbols and units
- a
- Original font bytes by weight
- b
- Subset font bytes by weight
- c
- Visits
- d
- Visits with all fonts cached (%)
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
Each uncached visit downloads every listed font weight. Cached visits transfer no font bytes. Both scenarios use the same cache-hit assumption. Confirm that the subset retains every required glyph; headers and revalidation are excluded.
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?
Original transfer (bytes); Subset transfer (bytes); Transfer saved (bytes); Reduction (%). 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: Each uncached visit downloads every listed font weight. Cached visits transfer no font bytes. Both scenarios use the same cache-hit assumption. Confirm that the subset retains every required glyph; headers and revalidation are excluded.
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.
Read the quality report →