Free calculators  ·  No sign-up  ·  Formulas sourced

Calculators that
show their working.

Space Atlas is a free library of online calculators and the guides behind them. Each page states the formula it uses and links to the body that sets it, so you can check the number instead of trusting it.

Browse the calculators How we source formulas

Maintained by Marcus Reed · Last reviewed 18 Sep 2026 · 6 categories · 271 calculators · Also in French

Where do you need a number?

Six categories. Every calculator is a live form with labelled inputs and the unit expected. If a value changes by country, carrier or year, the guide says so and links out.

See all calculators

How a Space Atlas answer is built

Three steps, in this order. A page that cannot complete all three is corrected or withdrawn.

The formula comes first

Each calculator implements a published formula or an institutional rule — a carrier tariff, a rate schedule, a standard test method, a specification. The page prints it above the result.

Your values, not our defaults

Defaults and pre-filled fields are illustrative. Fields carry their unit, because unit confusion is the most common source of a wrong result.

The figure is checked against its source

The guide links to the body that sets the number, and says what the number moves with — year, country, carrier, product tier. Where we cannot trace a figure, we delete it.

What makes an answer defensible

  • A named source. Not “experts say”. A tariff, standard or statute, linked so you can read it yourself.
  • A date. Last reviewed is printed on guides and policy pages; a stale page has not been re-checked.
  • A stated limit. Results are estimates. Where a lender, tax authority or carrier decides the final figure, we say so.
  • No invented experience. Our examples are worked arithmetic, not client stories or job titles. If you find one, report it and it goes.

Recent guides

Long-form explanations of one formula at a time, with a worked example you can recheck line by line.

What Space Atlas is not

Not professional advice
We are not a law, tax, accounting, insurance or medical practice, and nothing here is advice for your situation.
Not a quote or an approval
A result is a computed estimate from the numbers you enter — not an offer, a filing or an appraisal.
Not a frozen number
Rates, thresholds and fees change by year and by jurisdiction. Every guide points to the live source.
Not a black box
The formula and its source are on the page. You should never have to take a figure on trust.