Calculation Methodology
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This page explains how we build, document, and verify the math behind our tools so you can trust — and check — the results.
Formulas and sources
Each calculator uses a standard, widely accepted formula, which we print directly on the tool’s page along with the meaning of every variable. Converters use exact, internationally recognized conversion factors (for example, 1 inch = 2.54 cm exactly, and 1 kg = 2.2046226218 lb). When a value is defined by convention rather than measurement, we say so.
Rounding and precision
We calculate at full floating-point precision and round only for display. Where rounding matters (currency, measurements), we round to a sensible number of decimal places and note it. Because we round at the end rather than mid-calculation, a result you reproduce by hand may differ in the last digit if you round early.
Testing
Tools are checked against known reference values and edge cases (zero, negative, very large, and boundary inputs) before publishing. The worked examples shown on each page double as visible test cases: if our math ever drifts, those examples would be wrong too.
Estimates vs. exact values
Pure conversions and arithmetic are exact within rounding. Many real-world calculators (loans, savings, calorie needs) are inherently estimates: they model a simplified version of reality using the inputs you provide. We label these clearly and list the assumptions they make.
Updates and corrections
Each tool shows a “last updated” date. When a formula, factor, or assumption changes — or when a reader reports an error — we fix the tool and update that date. To report a problem, see our Correction Policy.