Convert between units instantly: length, weight, temperature, volume, area, and speed.
In 1999, NASA lost the Mars Climate Orbiter — a $327 million spacecraft — because one engineering team used metric units and another used imperial units, and nobody caught the mismatch. Unit conversion errors are not just inconvenient; in engineering, medicine, and science they can be catastrophic. This tool handles the math so you don't have to.
Every other unit conversion is a simple multiplication by a fixed ratio. 1 kilometer = 1000 meters, always. Temperature is different because the three scales (Celsius, Fahrenheit, Kelvin) have different zero points. Zero Celsius is not zero Fahrenheit. Zero Kelvin (absolute zero) is -273.15°C and -459.67°F.
The formulas: °F = (°C × 9/5) + 32. °C = (°F − 32) × 5/9. K = °C + 273.15. This is why temperature conversions feel unintuitive — you can't just multiply by a single number.
The US is one of only three countries (with Myanmar and Liberia) that hasn't officially adopted the metric system. This creates constant conversion needs for Americans working with international data, and for non-Americans working with US-sourced content. The most common conversions people need:
Storage units have a confusing dual standard. In decimal (SI): 1 KB = 1,000 bytes, 1 MB = 1,000,000 bytes. In binary (IEC): 1 KiB = 1,024 bytes, 1 MiB = 1,048,576 bytes. Hard drive manufacturers use decimal (makes drives look bigger). Operating systems traditionally used binary (Windows still does; macOS switched to decimal in 2009). This is why a "500 GB" hard drive shows as ~465 GB in Windows.
All conversions are calculated in your browser using JavaScript. Nothing is sent to any server.
The converter covers length, weight/mass, temperature, area, volume, speed, time, digital storage, and energy. Each category has all commonly used units including both metric and imperial systems.
Most unit conversions are simple multiplication (e.g., 1 km = 1000 m). Temperature conversions require addition and multiplication because the scales have different zero points. For example, Celsius to Fahrenheit is (C x 9/5) + 32, not just a ratio.
Conversions use standard internationally recognized conversion factors. Results are shown to several decimal places. For scientific or engineering work requiring extreme precision, verify against official standards like NIST.
Yes. All categories include both metric (SI) and imperial/US customary units. For example, length includes millimeters, centimeters, meters, kilometers alongside inches, feet, yards, and miles.
Mass is the amount of matter in an object (measured in kg or lbs) and does not change with gravity. Weight is the force gravity exerts on that mass and varies by location. In everyday use, the terms are used interchangeably, and this converter treats them as equivalent for practical purposes.