Methodology

Shared calculation engines

Every tool uses a small set of shared calculation modules rather than separate code on each page. The formula described on a page is the formula the tool runs, and reference tables on converter pages are generated by the same code as the converter.

Units and constants

Conversions use exact definitions where they exist, such as the international inch (25.4 mm), pound (0.45359237 kg), standard gravity (9.80665 m/s²) and the 2019 SI values of the elementary charge. Sources are mainly NIST Special Publication 811 and the BIPM SI Brochure; each converter page names its reference. US customary and Imperial units are kept separate where they differ. Units with special formulas — temperature offsets, reciprocal fuel economy and logarithmic decibels — are handled with their own equations rather than a simple factor.

Precision and rounding

Calculations use double-precision floating point. Results are rounded to 12 significant digits to remove binary rounding artifacts, then formatted for display; converter results show up to eight decimal places and switch to scientific notation for very large or very small values.

Validation

Inputs are checked before calculating. Invalid or physically impossible values (for example, temperatures below absolute zero, zero sound pressure, or division by zero) show a message instead of a misleading number.

How results are verified

The calculation modules have automated tests that compare results with known reference values, check conversions in both directions, confirm every unit round-trips through its base unit, and cover edge cases such as zero, negative and invalid inputs, very large and small values, leap years, month ends, overnight times and absolute zero. These tests are run by the site's developer when calculations change; they are not a guarantee that every possible input is correct.

Limits

Tools model standard formulas with the inputs you provide. They do not account for local codes, lender fees, product-specific coverage or other factors unless a page says so. See the Disclaimer.