Unit Conversion Calculator

Convert length, weight, volume, temperature, area and speed between common US and metric units.

Converted Result

160.9344 km

100 mi = 160.9344 km

Six categories

Common US and metric units

Standard conversions

Factors and temperature offsets

Works on any device

Mobile, tablet or desktop

How to Use the Unit Conversion Calculator

Choose a category, enter a value, then choose the From and To units. The result updates immediately when you type or change a unit. Swap Units exchanges the selected units while keeping your input value. Copy Result copies the displayed number and unit label. Changing category selects a suitable pair of units and keeps your entered value.

Formula and Explanation

Length, weight, volume, area, speed:
Result = Input × From-unit factor ÷ To-unit factor

Temperature:
°F = (°C × 9 ÷ 5) + 32
°C = (°F − 32) × 5 ÷ 9
K = °C + 273.15

Length, weight, volume, area and speed use fixed scale factors through a shared base unit. For example, one international foot is 0.3048 meters and one pound is 0.45359237 kilograms. Temperature needs offsets as well as scaling: convert Celsius and Fahrenheit using the formulas above, and add 273.15 to Celsius for Kelvin. Absolute zero is −273.15 °C, −459.67 °F or 0 K. Area factors apply to square units rather than ordinary lengths.

Volume uses US customary liquid measures: a cup is 8 US fluid ounces, not the 240 mL labeling cup or an imperial cup. Weight means mass here and uses avoirdupois ounces, not troy ounces. Acres use the international foot rather than the former US survey foot. Negative length and speed values can represent offsets or direction; mass, volume and area must be non-negative. Temperatures below absolute zero are rejected. Results use up to 12 significant digits, with scientific notation for very large or small values. Invalid numbers and results outside finite numeric range are rejected.

NIST: Unit conversion factors

Worked Examples

Length: 2.5 miles = 4.02336 kilometers. Weight: 16 US mass ounces = 1 pound. Volume: 1 US gallon = 3.785411784 liters. Temperature: 32 °F = 0 °C = 273.15 K. Area: 1 acre = 43,560 square feet. Speed: 60 mph = 96.56064 km/h. Reverse any example by swapping the selected units and entering its converted value.

Frequently Asked Questions

Which categories and units are supported?

Length includes mm, cm, m, km, inches, feet, yards and miles. Weight includes mg, g, kg, US mass ounces, pounds, US short tons and metric tonnes. Volume includes mL, L and US fluid ounces, cups, pints, quarts and gallons. Temperature supports Celsius, Fahrenheit and Kelvin; area supports square feet, square meters, square yards, acres and hectares; speed supports mph, km/h, m/s and knots.

Are the US and metric volume or weight units interchangeable?

They are different units with defined factors. One US liquid gallon is 3.785411784 liters, and one US customary cup is 236.5882365 mL. One US short ton is 2,000 pounds; a metric tonne is 1,000 kg. A mass ounce is different from a fluid ounce, and imperial liquid units are not supported.

Can I convert negative values and temperatures below zero?

Negative Celsius or Fahrenheit readings are valid down to −273.15 °C or −459.67 °F. Kelvin cannot be below zero. Signed length and speed values are accepted for directional measurements; negative weight, volume and area are rejected.

What do Swap Units and Copy Result do?

Swap Units reverses the From and To selections and recalculates the same input value. Copy Result copies the formatted result with its unit label. Display rounding is limited to 12 significant digits; the calculation uses the unrounded input and factors. If browser clipboard access is unavailable, select the result text and copy it manually.