What Is Numbat on david-peter.de?

Updated

Numbat is a high-precision scientific calculator with full support for physical units, listed on David Peter's personal site (david-peter.de) and hosted at numbat.dev. It is a command-line tool that runs both in the terminal and in the browser, and it is aimed at people who want unit-aware calculations rather than a graphical calculator interface.

What Numbat does

According to the site, Numbat is built around an interactive command-line interface. That is the main difference from many graphical calculators: instead of tapping buttons on a keypad, you type expressions and get results back.

Its stated capabilities are:

  • Physical units throughout: calculations carry units, so quantities are not treated as bare numbers.
  • Broad unit coverage: it understands all SI units, including metric and binary prefixes, as well as most US customary and imperial units.
  • Built-in math and constants: many predefined mathematical functions and physical constants are available.
  • User-defined variables and functions: you can define your own, so repeated or project-specific calculations can be packaged into named expressions.

Where it runs

Numbat runs in two environments:

Environment How you use it
Terminal Interactive command-line interface
Browser Same calculator, accessible without a terminal

The site does not describe installation steps, pricing, or account requirements, so those details are not established here. If you want to try it, numbat.dev is the entry point named on the page.

How it differs from a typical calculator

The distinguishing mechanism is unit-aware evaluation. A conventional calculator returns a number, and you are responsible for remembering whether it is meters, seconds, or dollars. Numbat's model keeps units attached to values, which matters when you combine quantities — for example, dividing a distance by a time to get a speed, or converting between metric and imperial measurements.

A concrete example of the kind of task this suits: computing a speed from a measured distance and duration, then converting the result into another unit system without redoing the arithmetic by hand. Because Numbat supports both SI and most US customary and imperial units, that conversion is part of the same calculation rather than a separate step.

Who it is for

Numbat fits people who already work at a command line or in a browser and want calculations that respect units — students and practitioners in science and engineering are the natural audience, given the site's framing of the tool. If you prefer a physical keypad, a graphical calculator, or a spreadsheet, Numbat's interactive command-line model is a deliberate departure from those.

Related projects on the same site

Numbat sits alongside David Peter's other open-source work, which is useful context if you like the command-line style:

  • Command-line programs: fd (a find alternative), hyperfine (benchmarking), bat (syntax-highlighted cat), hexyl (terminal hex viewer), pastel (color manipulation), and vivid (LS_COLORS generator).
  • cube composer: a puzzle game inspired by functional programming, written in PureScript.
  • quizzity and curiositY: additional projects listed on the page.

The site also notes that his open-source work is published on GitHub and his academic work on arXiv, and that he can be reached by email.