Formula Reference
Browse the curated formula pages currently approved for public discovery: BMI, percentage, area of a circle, compound interest, and mortgage.
5 Formulas
3 Categories
Sourced & Verified
Math
2Finance
2How to use these formula pages
Every formula page follows the same structure: the formula rendered in standard mathematical notation, a table defining each variable with its unit, a worked example with real numbers, and an interactive calculator that runs the same formula so you can check your own inputs immediately.
Use the reference when you need to cite or rearrange a formula — for homework, engineering notes, or documentation. Use the linked calculator when you just need the answer. Both views come from the same definition, so they can never disagree.
Values follow the conventions documented in our methodology, rounding policy, and sources and standards pages. If you find an error, the corrections policy explains how we handle fixes.
How these formula pages are built
A formula page documents one expression: what it computes, what each symbol means, the units it expects, and its source. It is the reference view of the registry entry behind the matching calculator.
Rearrangements are derived from the stored expression, so solving for another variable cannot fall out of sync with it.
Every page in this section carries:
- the expression in standard notation, with every symbol defined
- the units each variable is expected in
- common rearrangements solved for each variable
- a worked example with real numbers
- the reference the expression is taken from
Reading a formula page
Check units before algebra: most wrong answers from a correct formula come from feet where it wants metres, or a percentage where it wants a decimal fraction.
To solve for another variable, use the rearrangement on the page rather than rearranging by hand.
Where these tools stop
- A formula holds under the conditions it was derived for. Empirical relationships in particular have a stated valid range, and applying one outside that range returns a number without meaning.
- Constants embedded in a formula may be regional or era-specific. Where that is the case the page names the constant and its source rather than silently folding it into the expression.
The market in the URL controls the numbers: currency, measurement convention, and any regional rule that changes the calculation. The interface language is a separate browser setting that never changes a result — it translates the labels while the computation, its units and its sources stay as they are.
Checking our work
Where a page states a standard, constant or regulatory limit, it names the source so the figure can be traced back. The methodology page describes how tools are generated and validated, rounding policy documents how displayed values are rounded, and sources and standards lists the references behind the platform. If a figure looks wrong, the corrections policy explains how to report it and what happens next.