Mortgage payments, take-home pay, paint coverage, running pace, energy bills — and exactly how long to rest a steak, or how long a drink takes to get cold at the back of the freezer. The nuanced things you’d look up or find in a forum, all in one place. Free, in your browser.
Rule of the day · The Rulebook
Caffeine halves about every five hours, so a coffee at 3 pm is still about half in you at 8 pm
Caffeine halves about every five hours: a coffee at 3 pm is still about half in you at 8 pm, a quarter at 1 am and an eighth at 6 am.
Open the full Rulebook Exact tool: Caffeine CurveReal calculators linked up. Change one number and every step reworks, then open any tool with your numbers already in it.
Every area and tool on one living map. Hover to read, click to open.
Dealt fresh on every visit, and running the same verified physics as the full tools — click a mini to feature it above, or open the simulator for controls and scenarios.
The earth, the sky, and the clock - moist-air physics, solar geometry, and time across the globe.
Structural and mechanical reference - load, stress, and the standard checks that go with them.
The properties of the stuff itself — every element and what it is actually for, how a fluid behaves as it warms, how dense a gas is, and what really sets the strength of a concrete mix.
Circuits and magnetics - Ohm's law, power factor correction, transformer turns ratio, and wire sizing.
Everyday money math - what your money does while it sits, and what a loan really costs over time.
How things respond and how we steer them - feedback control and the limits of digital sampling.
The machines themselves - storage layout, networks, and the trade-offs of keeping data safe.
Real, live simulations you can nudge and watch respond - oscillation, chaos, motion under friction, and heat transfer.
Hands-on reference for around the house - paint, fixings, concrete, tea, coffee, grinding, eggs, and precision timing.
A scientific calculator that shows its own order of operations, trigonometry, a full 2D/3D geometry suite, and statistics with a genuinely random Galton board.
BMI on a full colour-coded chart, running/cycling/swimming pace, and calorie needs from a validated formula.
An instrument is a physics experiment you can hold. Notes named on the stave, pitch read to a fraction of a cent, chord shapes and scale positions worked out from the tuning itself, and beats placed on the audio clock rather than the browser's.
The classic games, played the way you know them and then taken apart: new rules, other board sizes, a coach that says why a move works, and puzzles made fresh from a number so a link shares the same one.
Open Puzzles and GamesStored on this device only. Nothing is sent anywhere.
Ranked by how many people starred each tool — one vote per browser, no account, and nothing about what you calculated.
Yes - every tool, no account, no paywall. There are no ads and no analytics running on this site today; see the privacy policy for exactly what that means and what would change first if that ever changes.
Each one is built from a real, cited formula or dataset - a physics equation, an engineering standard, published statistics - not a guess. Every tool's footer names its source, and most are verified against the source's own worked examples before publishing. See Sources for the full list.
No first-party cookies and no analytics. Calculator inputs stay in your browser. The optional Favourite star on a tool saves it for you locally and can add +1 to the public popular ranking - never the numbers you typed. See Privacy.
Yes, after your first visit. The site is installable as an app on desktop and mobile, and previously visited tools keep working offline.