Unit conversion factors and precision
Unit conversion changes the scale used to express a quantity, not the quantity itself. For units in a category with fixed conversion factors, the calculator converts the input to a shared reference scale and then to the chosen output unit. Temperature uses separate offset formulas because its scales have different zero points.
Examples
One international mile is exactly 1.609344 kilometers, so 5 miles is 8.04672 km. One kilogram is approximately 2.20462 pounds. These examples illustrate why it is important to choose the correct category and compare like-for-like quantities.
Data units use a chosen convention
This tool uses powers of 1024 for KB, MB, GB, and TB and for its Kbit, Mbit, and Gbit labels. Some storage and networking specifications use decimal multiples of 1000 instead. If the number is for a drive capacity, data plan, or network speed, check which convention the manufacturer or provider uses.
Displayed values are rounded for readability. For precise work, carry unrounded values through subsequent calculations where possible and round only at the end.
Tips for accurate results
Select the category first, such as length, weight, or volume, then pick the from and to units. For areas and volumes, remember that the conversion factor is squared or cubed. Some conversions, such as cups to grams, depend on the ingredient.
Common mistakes and limits
Check whether you mean US or imperial units, since gallons, pints, and ounces differ. Keep extra decimals during multi-step calculations and round at the end. A quick plausibility check can catch most input mistakes.
Learn more: Unit conversion: common mistakes and how to avoid them.