SuperCalc

Unit Converter

Convert between metric and imperial units instantly. Length, weight, temperature, speed, volume, area, data, and time — all in one place.

Unit Converter

Select a category, pick your units, and type a value to convert instantly.

Result

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How unit conversion works

Unit conversion is the process of expressing a quantity in a different unit of measurement without changing its actual value. At its core, every conversion multiplies by a ratio that equals 1 — for example, 1 km / 1000 m. The numerator and denominator are the same physical quantity, so the ratio is unity.

For most categories (length, weight, speed, volume, area, data, time), we define a base unit and store a conversion factor for every other unit. Converting from unit A to unit B means: multiply by A's factor to reach the base, then divide by B's factor.

Temperature is the exception — it uses formulas with offsets rather than simple ratios. Converting Celsius to Fahrenheit requires multiplying by 9/5 and adding 32. Kelvin is Celsius shifted by 273.15 degrees. These formulas are exact; no approximation is involved.

FAQ

How do unit conversions work?
Each category has a base unit (e.g. meter for length, kilogram for weight). Every other unit in that category has a conversion factor relative to the base unit. To convert between two units, we multiply the input by the source unit's factor to get the base value, then divide by the target unit's factor.
What is the difference between metric and imperial?
Metric (SI) is the international standard based on powers of 10 — meters, kilograms, liters. Imperial (also called US customary) uses traditional units — miles, pounds, gallons. Most of the world uses metric; the US, Liberia, and Myanmar still use imperial for everyday measurements.
How do I convert temperature?
Temperature conversions use formulas, not simple ratios. Celsius to Fahrenheit: multiply by 9/5 and add 32. Fahrenheit to Celsius: subtract 32 and multiply by 5/9. Celsius to Kelvin: add 273.15. These formulas are exact — no rounding needed.
What is the difference between GB and GiB?
GB (gigabyte) uses decimal prefixes: 1 GB = 1,000,000,000 bytes. GiB (gibibyte) uses binary prefixes: 1 GiB = 1,073,741,824 bytes (2^30). Hard drive manufacturers use GB; operating systems often report storage in GiB, which is why a '500 GB' drive shows up as ~465 GiB.
Are the conversions exact?
Many conversions are exact by definition (e.g. 1 inch = 25.4 mm exactly). Others, like nautical miles, use the internationally agreed value. Results are displayed with up to 10 significant digits. For scientific work requiring higher precision, consult NIST reference values.
Is my data sent anywhere?
No. Every conversion runs entirely in your browser using JavaScript. Nothing is sent to any server. Your last inputs are saved in your browser's local storage so they survive a page refresh — that data never leaves your device.

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