Units carry themselves
Every quantity tracks its units. Mix metres, mm, GPa and kN and the answer comes out in the unit you ask for — dimension mismatches are caught before they bite.
engineering calc / unit-aware / live worksheet
Napkin math,
engineered.
NapkinCalc is a live calculation worksheet for engineers and students. Write the math the way you would on paper — with real units — and it solves as you type, in dependency order, every time you change a number.
runs in the browser / free in beta / no install
L := 3·m span
w := 12·kN/m distributed load
E := 200·GPa Young's modulus
I := 85·10⁶·mm⁴ second moment
δ := w·L⁴ / (8·E·I) = 7.15·mm max deflection
why it matters
Change w from 12 to 18 kN/m and δ updates the instant you finish typing — units, decimals and all the way down the sheet.
- dimension-checked
- dependency-ordered
- exportable to PDF
- 200+ units & constants
- live recalculation
- 0 syntax to memorize
- PDF export to hand in
the core idea
A calculator that behaves like an engineer.
Spreadsheets hide the formula and lose the units. Code makes you fight syntax. NapkinCalc keeps the math visible, the units honest, and the result one keystroke away.
Recalculates as you think
Change one input and the whole sheet updates instantly, in dependency order. No "run" button, no stale numbers, no spreadsheet cell-chasing.
Math that reads like math
Real notation — fractions, roots, subscripts, summations — typed naturally. Your worksheet looks like the page you would have written by hand.
Numeric and symbolic
Solve, simplify and rearrange symbolically, then drop in numbers for a result. Vectors, matrices and data tables included.
units are the feature
Units aren't a comment. They're the math.
A length is metres, a force is newtons, a stress is pascals — and NapkinCalc treats them that way. Quantities carry their dimensions through every operation, so a unit slip becomes an error you see, not a number you ship.
12 kN/m×(3 m)⁴÷8·E·I=7.15 mm//guess the unit
write to result
Write, compute, share.
- 01write
Write the math
Define variables with :=, build expressions the way you would on paper. Units are part of the value, not a comment.
- 02compute
Watch it solve
Results appear inline and recompute live. Forward references and dependency order are resolved for you.
- 03share
Hand it in or hand it off
Export a clean PDF of the full worked solution — auditable for a reviewer, gradeable for a professor.
Hand calcs you can defend.
Sizing, loads, flow, tolerances — auditable worksheets where every assumption and unit is on the page. Change an input and the whole calc re-derives, so a design review reads top to bottom without surprises.
Homework that shows its work.
Type the problem the way the textbook writes it, check your units automatically, and export a clean PDF of the full solution. Learn the method instead of wrestling a graphing calculator.
simple pricing
Engineering math without the engineering-software bill.
Legacy Mathcad-style tools cost hundreds a year and want an install and a licence server. NapkinCalc opens in a tab.
legacy calc software
$$$/yr
Per-seat subscriptions, desktop installs and licence servers for math you do every day.
napkincalc
Freein beta
Open a worksheet in the browser. Units, live recalculation and PDF export included.
what you get
Free, today
- Unit-aware live worksheets
- Numeric & symbolic solving
- Vectors, matrices & data tables
- PDF export of the full solution
before you ask
Questions, answered.
Do I have to learn a syntax?
No. You type math the way you would write it — assignments with :=, fractions, exponents, subscripts and units. The worksheet renders it as proper notation as you go.
How do units work?
Units are attached to values, not bolted on as text. Add a length in mm to one in m and it just works; multiply a force by a distance and you get a moment. Ask for the result in any compatible unit.
Who is it for?
Practising engineers who need auditable, unit-safe hand calcs, and students who want their homework to read like a worked solution instead of spreadsheet cells.
Is it free?
NapkinCalc is free while in beta. It runs in your browser — open a worksheet and start calculating, no install required.
do the math
Stop guessing the units.
Open a worksheet, define your first variable, and watch the answer fall out — carried units and all.