Convert length, weight, temperature, and volume units
Unit conversion looks trivial and has historically caused expensive mistakes. NASA's 1999 Mars Climate Orbiter was lost because thrust data was provided in pound-force-seconds but interpreted as newton-seconds, a 4.45x difference; the probe entered the Martian atmosphere at the wrong altitude and disintegrated. The conversion factor itself was not hard, it is a single multiplication, but trusting that one team's "units" matched another team's assumption is where real systems fail. This converter handles the arithmetic correctly across the common measurement domains: length (meters, feet, inches, miles, nautical miles), weight/mass (kilograms, pounds, ounces, stones, tons), temperature (Celsius, Fahrenheit, Kelvin, Rankine), volume (liters, gallons, fluid ounces, cubic meters), speed (m/s, km/h, mph, knots), area (m², ft², acres, hectares), and data storage (bytes, KB, MB, GB, with attention to the decimal-vs-binary distinction). Temperature conversion is the one that trips people up most often because the scales have different zero points and different degree sizes. Celsius to Fahrenheit is `F = C * 9/5 + 32`not just a multiplication. The freezing point of water is 0°C / 32°F and the boiling point is 100°C / 212°F, which means a 1°C change is 1.8°F. Kelvin is absolute-zero-based (0 K = -273.15°C) and uses Celsius-sized degrees. For weather and cooking, 0°C = 32°F is the everyday reference; for scientific work, Kelvin is the right choice because it supports multiplication without negative-value weirdness.
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A spec sheet lists a top speed of 100 km/h and your US-facing copy needs mph (and the physics needs m/s).
Input
100 km/h
Converted
62.137 mph 27.778 m/s 91.134 ft/s
Conversions use exact definitional factors (1 mile = 1.609344 km exactly), not rounded approximations, so chained conversions do not accumulate error. The tool covers length, mass, temperature, speed, data, and more, handling the cases people get wrong, like temperature being an offset scale, not a simple ratio.
Unit conversion looks trivial and has historically caused expensive mistakes. NASA's 1999 Mars Climate Orbiter was lost because thrust data was provided in pound-force-seconds but interpreted as newton-seconds, a 4.45x difference; the probe entered the Martian atmosphere at the wrong altitude and disintegrated. The conversion factor itself was not hard, it is a single multiplication, but trusting that one team's "units" matched another team's assumption is where real systems fail. This converter handles the arithmetic correctly across the common measurement domains: length (meters, feet, inches, miles, nautical miles), weight/mass (kilograms, pounds, ounces, stones, tons), temperature (Celsius, Fahrenheit, Kelvin, Rankine), volume (liters, gallons, fluid ounces, cubic meters), speed (m/s, km/h, mph, knots), area (m², ft², acres, hectares), and data storage (bytes, KB, MB, GB, with attention to the decimal-vs-binary distinction). Temperature conversion is the one that trips people up most often because the scales have different zero points and different degree sizes. Celsius to Fahrenheit is `F = C * 9/5 + 32`not just a multiplication. The freezing point of water is 0°C / 32°F and the boiling point is 100°C / 212°F, which means a 1°C change is 1.8°F. Kelvin is absolute-zero-based (0 K = -273.15°C) and uses Celsius-sized degrees. For weather and cooking, 0°C = 32°F is the everyday reference; for scientific work, Kelvin is the right choice because it supports multiplication without negative-value weirdness.
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Data storage units have a famous dual standard. Hard drive manufacturers use decimal (SI) units where 1 KB = 1,000 bytes, 1 MB = 1,000,000 bytes, 1 GB = 1,000,000,000 bytes. Operating systems (Windows, macOS, and Linux file managers) historically used binary units where 1 KB = 1,024 bytes (2^10), 1 MB = 1,048,576 bytes (2^20), 1 GB = 1,073,741,824 bytes (2^30). The difference grows with scale: at the terabyte level, 1 TB decimal = 0.909 TiB binary, which is why a "1 TB drive" shows up as 931 GB in your file manager when using binary interpretation. IEC standardized binary prefixes (KiB, MiB, GiB, TiB) specifically to resolve this ambiguity, but adoption is uneven, Linux tools use them correctly, macOS and Windows mostly still say "GB" when they mean "GiB".
Length and weight conversions are exact rational numbers in the SI system (1 inch is exactly 25.4 mm by international agreement since 1959) but historical units like "foot" have had multiple definitions over time (US survey foot vs international foot differ by about 2 parts per million, which matters for surveying but not for anything else). This converter uses the international-foot and modern-pound definitions consistently. Nautical units use different base conversions from land units: 1 nautical mile = 1,852 meters exactly (based on one minute of latitude along any meridian), and 1 knot = 1 nautical mile per hour. Aviation and maritime use nautical miles; everything else on the ground uses statute miles.
Area unit conversions are where dimensional thinking matters. 1 square mile is NOT 5280 square feet, it is 5280 squared, or 27,878,400 square feet, because area scales with the square of linear measure. Volume scales with the cube. This is the source of many errors in unit conversion when people try to "just multiply by 5280" from miles to feet for an area; converting the length dimensions separately and then multiplying area is correct but error-prone. The converter handles the power correctly so m² to ft² uses (3.28084)² = 10.764 as the factor, not 3.28084. For most everyday unit conversions you do not need to think about this, just pick source and target, but it is worth understanding if you are ever debugging a custom conversion and getting numbers that are off by a power of 10 or more.
Conversions use standard conversion factors and are accurate to many decimal places. Results are displayed with reasonable precision.
Conversions run on your device in JavaScript. The values you enter are never sent over the network.