Unit conversion calculator

Common length conversions

Length conversions work by multiplying a value by a fixed factor, since all length units share the same starting point of zero. A few conversions come up often enough to be worth memorizing:

• 1 meter = 3.28 feet
• 1 mile = 1.61 kilometers
• 1 inch = 2.54 centimeters

The calculator above supports meters, feet, inches, miles, kilometers and centimeters, converting through a common base unit of meters so any pair can be combined directly. Each unit is stored as a factor relative to one meter, so converting from any unit to any other unit is a two-step process: divide by the factor of the unit you are converting from to get a value in meters, then multiply by the factor of the unit you want. This is why the same lookup table can handle all fifteen possible pairs among the six length units without needing a separate formula for each combination.

Length conversions come up constantly in everyday situations: comparing a recipe written in centimeters to a ruler marked in inches, checking whether furniture measured in feet will fit through a doorway measured in meters, or converting a race distance from kilometers to miles. Because the relationship between any two length units is a fixed ratio, these conversions are always exact multiplication, with no rounding surprises beyond the precision of the factor itself.

Common weight conversions

Weight conversions follow the same simple multiplication logic as length. Two useful ones to remember:

• 1 kilogram = 2.20 pounds
• 1 pound = 16 ounces

The calculator supports kilograms, pounds, ounces and grams, converting through kilograms as the base unit, using the same divide-then-multiply approach used for length. Weight conversions matter for cooking, where a recipe from a different country may list ingredients in grams while your kitchen scale reads in ounces, for shipping, where carriers price by pound or kilogram depending on the country, and for tracking body weight across regions that use different default units.

Why temperature conversion isn't just multiplication

Unlike length and weight, temperature scales do not all start counting from the same zero point. Celsius sets zero at the freezing point of water, Fahrenheit sets zero at a different reference entirely, and Kelvin sets zero at absolute zero, the coldest physically possible temperature. Because the scales are offset from each other, converting between them requires adding or subtracting a number in addition to scaling, not just multiplying by a ratio.

The formulas used by this calculator are: Celsius to Fahrenheit is C times 9/5 plus 32. Fahrenheit to Celsius is F minus 32, times 5/9. Celsius to Kelvin is C plus 273.15. Kelvin to Celsius is K minus 273.15. Fahrenheit to Kelvin and Kelvin to Fahrenheit are handled by converting through Celsius first, applying both formulas in sequence.

As a check: 0 degrees Celsius equals 32 degrees Fahrenheit and 273.15 Kelvin, the freezing point of water. 100 degrees Celsius equals 212 degrees Fahrenheit and 373.15 Kelvin, the boiling point of water at sea level.

The calculator handles Fahrenheit to Kelvin and Kelvin to Fahrenheit by routing through Celsius as an intermediate step rather than using a direct formula. This keeps the logic simple and avoids the risk of getting the combined offset and scaling factor wrong when deriving a Fahrenheit-to-Kelvin formula from scratch. Since Celsius sits in the middle of both conversion paths, converting through it first and then out to the target unit produces the same result as a direct formula would, with less room for error.

Frequently asked questions

How do I convert Celsius to Fahrenheit?

Multiply the Celsius value by 9/5, then add 32. For example, 20 degrees Celsius times 9/5 is 36, plus 32 equals 68 degrees Fahrenheit.

How do I convert Fahrenheit to Celsius?

Subtract 32 from the Fahrenheit value, then multiply by 5/9. For example, 68 degrees Fahrenheit minus 32 is 36, times 5/9 equals 20 degrees Celsius.

How many feet are in a meter?

One meter equals approximately 3.28 feet. To convert meters to feet, multiply the meter value by 3.28.

How many pounds are in a kilogram?

One kilogram equals approximately 2.20 pounds. To convert kilograms to pounds, multiply the kilogram value by 2.20.

Why can't I just multiply to convert temperature?

Celsius, Fahrenheit and Kelvin scales start counting from different zero points, so converting between them requires adding or subtracting an offset in addition to scaling, unlike length or weight conversions which are a simple multiplication.