Unit conversion expresses the same quantity using a different unit. The amount does not change; only the scale used to describe it changes. Keeping units visible during a calculation helps catch mistakes.
Use a Conversion Factor
A conversion factor is a ratio equal to one, such as 100 centimeters per meter. To convert 2.4 meters to centimeters, multiply 2.4 meters by 100 centimeters per meter. The meter units cancel, leaving 240 centimeters.
For compound units, convert each part carefully. Speed, for example, combines distance and time, so changing kilometers per hour to meters per second requires converting both distance and time. Temperature scales also use offsets, so Celsius-to-Fahrenheit conversion is not a simple multiplication by a constant.
Keep Precision in Mind
Rounding too early can affect the final answer. Keep extra digits during intermediate steps, then round to a precision appropriate for the measurement and task. The number of displayed decimal places does not make an imprecise measurement more accurate.
Use the Unit Converter for common measurement conversions, then check that the selected categories and units match your problem. For engineering, medical, or regulated work, verify results against the applicable standard or an authoritative reference.