Definitions, precision and limits

The engine represents decimal inputs and unit factors as ratios of integers. This avoids the usual binary floating-point loss in calculations such as data-size conversion. Repeating decimal results are rounded only for display, using half-up rounding of the magnitude, with ties away from zero.

Definitions used

• International inch: exactly 0.0254 m. International foot: exactly 0.3048 m. Acre: 43,560 international square feet, exactly 4046.8564224 m². The obsolete US survey foot is not used.
• Avoirdupois pound: exactly 0.45359237 kg. Ounce: 1/16 pound. No troy units are included.
• US liquid gallon: 231 cubic inches, exactly 3.785411784 L. Imperial gallon: exactly 4.54609 L. US customary cup: 1/16 US gallon. The separately labelled metric cup is 250 mL.
• Thermochemical calorie: 4.184 J. Mechanical horsepower: 550 ft·lbf/s. Standard gravity: 9.80665 m/s². Standard atmosphere: 101325 Pa. Torr: 1/760 atmosphere.
• Day: 86400 seconds. This is a duration conversion, not calendar arithmetic; leap seconds, months and time zones are not calculated.

Precision is not measurement certainty

The selector controls significant digits, not decimal places. Exact and Rounded describe numerical display relative to these definitions. They do not imply that an instrument or an estimate is accurate to 30 digits. Very small or large results use scientific notation. Input is bounded to 100 numeric digits and exponents from −100 to +100 for predictable browser work.

Supported scope

Fourteen categories cover data size, data rate, length, mass, temperature, area, volume, speed, time, pressure, energy, power, frequency and force. Values are converted only within one category. There is no currency feed, speed test, density-based mass-to-volume conversion or calendar calculator.

Sources: NIST SI conversion factors and NIST binary prefixes. Constants derived from exact definitions are retained as fractions or full decimal values rather than copying rounded table entries.