# Sizewise Big Number Explainer

> What does a googol, 2^64 or 8 billion really mean? Names, digits and counting time. Explains any big number written as digits, words, scientific notation, powers or factorials: exact digits, scientific notation, the short- and long-scale names, how long counting to it takes, how high a stack of banknotes it makes and which famous numbers are close.

Part of usefulweb.app (https://usefulweb.app/). Part of [Sizewise](https://sizewise.usefulweb.app/) (ownerApp: sizewise). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://sizewisebignumber.usefulweb.app/ (interactive tool at https://sizewisebignumber.usefulweb.app/tool)
- JSON API: POST https://sizewisebignumber.usefulweb.app/api/v1/calculate with a JSON object of inputs (schema: https://sizewisebignumber.usefulweb.app/api/v1/tool)
- OpenAPI: https://sizewisebignumber.usefulweb.app/openapi.json
- MCP (Streamable HTTP): https://sizewisebignumber.usefulweb.app/mcp - tool `sizewise_big_number`

## Inputs
- number (text): Number - For example 8 billion, 8117059282, 6.02e23, 3 × 10^8, 2^64, 52! or googol.
- perSecond (number): Counting speed

## Method
- Numbers are kept exact as big integers up to 20 000 digits (factorials up to 3 000! exactly, larger ones from the Stirling series); beyond that only the logarithm is kept.
- Names follow the Conway–Wechsler system for 10^(3n+3) on the short scale (English, US) and 10^(6n) / 10^(6n+3) (-illion / -illiard) on the long scale used in most of continental Europe, with the traditional dictionary spellings from 10^48 to 10^60.
- Counting time uses the Julian year of 365.25 days and the age of the universe from Planck 2018 (13.787 billion years). The banknote stack uses 0.0043 in (0.109 mm) per US note.

## Limits
- Number names beyond the dictionary ones are systematic constructions; dictionaries rarely list them.