Libre Calculator

The universe in numbers.
Building the world's best calculators, free and open source.

Website · Download · Calculator packs · Get started · Ways to help · Docs

Why Libre Calculator

A compound interest calculator showing its inputs, final balance and formula

Explains every answer

Each result shows the steps that produced it, with a diagram and a short lesson underneath.

Steps use your inputs, not a generic example
Answer, steps and diagram come from one calculation
Lessons explain the idea behind the formula

Calculator tiles for health, construction and cooking, each with a pack switch

Packs you switch on

Core is always on. Turn on health, cooking, construction and the rest when you need them.

Every calculator has its own page on the web
Active packs are cached for offline use
The catalog is built to grow to thousands

The website in a browser window next to the desktop quick panel and its keyboard shortcut

Web and desktop

Use it at librecalculator.com, or run the desktop app. Cmd/Ctrl Shift C opens a quick panel from anywhere to find a calculator.

Static website, one page per calculator
Desktop app built with Tauri
Same calculators and design on both

A numeric contract card listing fixtures such as the square root of 9 equals 3, each checked

Exact by contract

Engines are pure functions with written numeric contracts and fixture tests. Arithmetic runs on 50-digit decimals and is rounded only for display.

Contracts per domain in docs/
Every engine has fixture tests in bun test
Invalid input fails clearly instead of guessing

Desktop app

Every calculator in a window of its own. Press Cmd/Ctrl Shift C in any app, type a few letters, and the calculator opens.

Free and open source. librecalculator.com/download picks the right file for your computer.

Calculator packs

See every calculator

Pack	Calculators
Core	Percentage, Percentage change, Fraction, Unit conversion, Area, Volume, Pythagorean theorem, Compound interest, Loan payment, Tip splitting
Construction	Concrete slab, Paint, Flooring, Roof area, Tile, Board foot
Cooking and food	Recipe scaling, Cups to grams, Oven temperature, Baker's percentage, Calories per serving
Date and time	Age, Date difference, Days until, Work hours, Time zone converter
Education	GPA, Grade, Final grade, Test score
Finance	Mortgage, Savings, ROI, Salary to hourly, Margin and markup, Inflation, Retirement savings
Geometry	Rectangle, Triangle, Circle, Sphere, Cylinder
Health and body	BMI, Resting energy (BMR), Daily energy (TDEE), Macros, Body fat estimate, Water intake, Weight at a chosen BMI
Math and everyday	Discount, Mean, median and mode, Standard deviation, Ratio, Scientific functions, Random number picker, Fuel economy
Physics	Speed, Force, Kinetic energy, Power, Density, Pressure
Statistics	Z-score, Confidence interval, Probability, Weighted average
Units and conversion	Length, Mass and weight, Temperature, Speed, Time duration, Cooking measures

Get started

The quickest way is the website: librecalculator.com.

Or get the desktop app for macOS, Windows (x64 and ARM) and Linux (deb, rpm and AppImage, x64 and ARM). Every build is also on the releases page.

To run it locally you need Bun 1.4.2 and Node 24.21.0.

git clone https://github.com/tonyzedginidze/librecalculator.git
cd librecalculator
bun install --frozen-lockfile
bun run dev            # website at http://localhost:4321
bun run dev:desktop    # desktop app (needs the Tauri prerequisites)

Add a calculator

New calculators start from one command. The generator is the registry, so nothing needs wiring by hand.

bun run new <id> [category]

Then replace the cloned engine, lesson, strings and view, and add the tile illustration. docs/new-calculator.md has the full checklist and the definition of done.

Before opening a pull request, all of these must pass:

bun run generate && bun run check:generated && bun run check:web-topics
bun run content-check && bun test && bun run typecheck && bun run lint
bun run build:web

How it is built

Path	What lives there
`packages/calculators`	Pure calculation engines and their tests
`packages/content`	Lesson text
`packages/i18n`	Every user-visible string
`packages/dom-ui`	Shared React calculator views
`packages/design`	Design tokens and styles
`packs/`	Pack manifests that group calculators
`apps/web`	Astro website, one page per calculator
`apps/desktop`	Tauri app with the quick panel

More in docs/architecture.md, docs/packs.md and docs/design-system.md.

Ways to help

You don't need to write code to make Libre Calculator better.

	How
Star the repo	A star takes one second and is the clearest sign the project is worth building. It helps people find Libre Calculator in GitHub search and trending lists, brings in more reviewers and contributors, and tells us which direction to keep growing.
Review a calculator	Pick one you know well and check its answer, steps and lesson. If a number, unit or explanation is off, open an issue with the inputs you used.
Suggest a calculator	Tell us what you wanted to calculate and couldn't. Real questions make the best calculators.
Improve a lesson	Clearer wording, a better example or a common mistake worth mentioning. Lessons live in `packages/content`.
Translate	All text already lives in `packages/i18n`, ready for other languages. Translation isn't open yet; tell us which language you'd help with so we can start there.
Draw a tile	Each calculator has a small flat illustration. docs/tile-illustrations.md has the house style.
Report a bug	Wrong results, broken layouts and accessibility problems all count.
Try the desktop app	Run it on your system and tell us what breaks or feels slow.
Share it	Send a calculator to a friend, a teacher or a colleague who would use it.
Build a calculator	Follow Add a calculator. Open an issue first so we can agree on scope.

Contributors

_{README art is rendered from the live site with bun run build:web && bun run readme:art.}