NapkinCalc is a live calculation worksheet for engineers and students — the back-of-the-napkin math you'd scribble on paper, except it actually solves itself. You write expressions with real units, and the whole sheet recomputes in dependency order the moment you change a number.
The problem
Spreadsheets hide the math behind cell references, and a scientific calculator forgets everything the second you clear it. Real engineering math lives somewhere in between: a handful of named quantities, carrying units, that feed into one another. NapkinCalc is built for exactly that middle ground.
How it works
- Unit-aware from the ground up.
L := 3·mandw := 12·kN/maren't strings — they're typed quantities. Multiply, divide, and the units come along; mix incompatible ones and it tells you. - Reactive evaluation. Change an input and every downstream value updates instantly, in the correct dependency order — no "recalculate" button, no stale cells.
- Reads like paper. Definitions, intermediate results, and final answers stack down the page the way you'd actually work a problem by hand.
- Runs in the browser. No install, nothing to configure — open a tab and start writing.
Highlights
- Worksheets you can save and reopen (e.g.
cantilever-deflection.ncalc) - Inline annotations so a sheet documents itself
- Decimals, units, and dependencies update together on every keystroke
Stack
Built on SvelteKit and TypeScript, with a unit-aware evaluation engine driving the live worksheet. Deployed on the edge.