calculatorkong

About & methodology

Accurate by design.

Calculator Kong is a precision toolkit of 101+ free calculators across nine categories — finance, health, math, construction, dates & time, unit conversion, science, text & code and everyday life. Every result is grounded in a published formula or an industry-standard library — never guesswork.

Standard formulas

Each tool implements a published, widely-accepted formula — and shows it to you.

Tested libraries

Money and date math run on battle-tested libraries (Formula.js, date-fns), not hand-rolled code.

Cross-referenced

Constants and coefficients are checked against authorities like WHO and NASA (see below).

Formulas & sources

The standards and authoritative references behind our calculators. Links open the source.

Health & fitness

Money & finance

Science & space

Units & conversions

Text, code & everyday

Dates & math

Our principles

Free forever

No accounts, no paywalls, no limits.

Private

Every calculation runs in your browser — your inputs never leave your device.

Fast

Lightweight static pages that load instantly.

Works offline

Installable as an app — every tool runs without a connection.

Frequently asked questions

Is Calculator Kong really free? +

Yes — every calculator is free forever, with no account, no sign-up and no paywall.

How accurate are the calculators? +

Each tool uses a published, widely-accepted formula or a battle-tested library (Formula.js for money, date-fns for dates), and the physical constants are cross-referenced against authorities such as the WHO and NASA — see the Formulas & sources list above.

Is my data private? +

Completely. Every calculation runs locally in your browser, so the numbers you enter never leave your device or reach a server.

Can I switch between metric and imperial units? +

Yes. Calculators that use measurements have a Metric/Imperial toggle in the tool bar, and each field lets you pick its own unit (e.g. cm, m, ft & in) and type values directly.

Can I change the currency? +

Yes — money calculators include a currency selector in the tool bar, and the input ranges scale sensibly to the currency you choose.

Can I share or embed a calculator? +

Yes. Share gives you a link that preserves your values plus a branded result image, Get widget gives you an embed snippet for your own site, and Pop out floats the calculator in an always-on-top mini window — see the <a href="/widgets/">widgets page</a> for a walkthrough.

Does Calculator Kong work offline? +

Yes — the site is an installable web app. Use the Install app button in the footer (or your browser’s install prompt) and every calculator keeps working without a connection.

How do I request a new calculator or report a problem? +

Head to the contact page and send us a note — we add and refine tools based on what people ask for.

Results are estimates provided for informational purposes only and are not a substitute for professional financial, medical, or engineering advice. Spotted an issue or want a new calculator? Get in touch.