How we build our calculators

Start with the method

Every calculator identifies its inputs, units, and mathematical relationship. Our articles explain where a relationship is useful and what assumptions it makes. Every calculator article includes academic or government references at the bottom. Source notes distinguish established formulas from illustrative estimates and planning assumptions.

Check the calculation

We test our calculation code against independently worked examples and check invalid inputs such as impossible proportions or negative dimensions. Results are rounded for display; intermediate calculations generally retain more precision.

Testing helps find mistakes, but does not certify a model for every use. Our tools are not laboratory instruments, veterinary assessments, or professional engineering evaluations.

Understand uncertainty

Some relationships are exact within a mathematical model, such as converting a circumference to a circular diameter. Others, including animal growth and tree age, are estimates based on averages. An exact-looking number should not be mistaken for an exact prediction.

For a consequential decision, check the inputs, assumptions, and result against an appropriate primary reference or qualified professional. An educational calculator should support your understanding, not replace necessary observation or expertise.

Keep explanations transparent

We write our explanations in our own words and distinguish worked examples from personal recommendations. Our tools run in your browser, making it easy to change an input and see what happens without sending it to our server.