Free Unit Converter
Pick a category, enter a value, and choose the units to convert from and to. Every conversion uses exact defined factors.
This free unit converter handles length, weight, temperature, and volume with exact conversion factors: one inch is defined as exactly 2.54 centimeters, one pound as exactly 453.59237 grams, and one gallon as exactly 3.785411784 liters. Temperature conversions use the standard offset formulas between Celsius, Fahrenheit, and Kelvin.
Conversions use internationally defined exact factors. Cooking volume conversions use US customary units; results are for general use, not legal metrology.
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How unit conversion works
Unit conversion is multiplication by a defined ratio. To convert miles to kilometers, you multiply by the exact definition: one international mile equals 1,609.344 meters, so one mile is 1.609344 kilometers. Every conversion in this tool is a chain of such exact definitions, never an approximation.
The metric system makes conversion trivial because it is decimal: 1 kilometer is 1,000 meters, 1 meter is 100 centimeters. Imperial units are historical: 12 inches to a foot, 3 feet to a yard, 1,760 yards to a mile, 16 ounces to a pound. Converting within imperial means multiplying or dividing by these odd ratios, which is exactly the arithmetic this tool does for you.
Temperature is the special case because the scales have different zero points, not just different sizes. Converting Celsius to Fahrenheit is multiply by 9/5 then add 32; Fahrenheit to Celsius is subtract 32 then multiply by 5/9. Kelvin shifts Celsius by 273.15 with no scaling. You cannot convert temperature with a single multiplication the way you convert length.
Precision deserves a note. Defined conversions like inches to centimeters are exact: 1 inch is exactly 2.54 cm by international agreement. Measured conversions, like a cup of flour to grams, are approximate because volume and weight relate through density. This tool converts volume to volume and weight to weight exactly, and does not pretend a cup of flour has a fixed gram weight.
A practical tip: convert once, at the end. Chaining rounded intermediate conversions accumulates rounding error. This tool converts directly from your source unit to your target unit in one step, then rounds only the displayed result.
Unit conversion questions
How many ounces are in a pound?
Exactly 16 ounces in a pound, by definition. That gives one ounce as 28.349523125 grams and one pound as 453.59237 grams. The common kitchen confusion is fluid ounces (volume) versus ounces (weight): 8 fluid ounces of water weighs about 8 ounces, but 8 fluid ounces of flour weighs much less.
What is the Celsius to Fahrenheit formula?
Multiply Celsius by 9/5 and add 32: F = C x 9/5 + 32. So 20 degrees Celsius is 68 Fahrenheit, and 0 Celsius is 32 Fahrenheit. To go the other way, subtract 32 and multiply by 5/9: C = (F - 32) x 5/9.
How many feet are in a mile?
Exactly 5,280 feet per mile (1,760 yards times 3 feet per yard). For reference, a kilometer is 3,280.84 feet, which is why a mile works out to about 1.609 kilometers.
What is the difference between metric and imperial?
The metric system is decimal: every conversion is a power of 10, and it is the global standard for science and most countries. The imperial (US customary) system uses historical ratios like 12 inches to a foot and 16 ounces to a pound, and it persists mainly in the United States for everyday measurement.