unitconversions.app is a free online unit conversion tool that lets you instantly convert between hundreds of units across 14 categories: length, weight/mass, temperature, volume, area, speed, time, digital storage, pressure, energy, frequency, angle, fuel economy, and cooking. There are no accounts, no sign-ups, and no conversion limits. Every tool on the site works immediately, in your browser, with no installation required.
The world uses two major measurement systems — the metric system (SI), used by nearly every country on Earth, and the US customary system, used primarily in the United States. These systems differ in their units for almost every physical quantity: kilometers versus miles, kilograms versus pounds, liters versus gallons, Celsius versus Fahrenheit. People cross these boundaries constantly: cooking from a foreign recipe, reading international news, buying imported goods, traveling abroad, working with colleagues in other countries, or studying science and engineering. Unit conversion is a universal need that touches daily life in ways most people don't consciously notice. We built unitconversions.app to make that need trivially easy to satisfy — fast, accurate, and free.
Unit converters serve an enormous range of users. Students encounter metric units in science classes while living in a country that uses customary units, requiring constant translation. Home cooks and bakers adapt international recipes that use grams, milliliters, and Celsius when their kitchen tools measure in cups, ounces, and Fahrenheit. Travelers crossing borders encounter speed limit signs, temperature forecasts, and fuel prices in unfamiliar units. Engineers, architects, and scientists routinely work across measurement systems when collaborating internationally or reading technical literature. Online shoppers buying from foreign retailers must interpret clothing sizes, product weights, and screen dimensions in metric terms. Healthcare professionals and patients convert medical measurements — body weight for drug dosing, blood pressure in mmHg versus kPa, temperature in Celsius versus Fahrenheit. In short, almost anyone who encounters the wider world beyond their home country needs unit conversion tools regularly.
All conversions run entirely in your browser using pure JavaScript math with hardcoded, internationally accepted conversion factors. No data is ever sent to a server. You can verify this by opening your browser's Network tab — you will see zero outbound requests when you perform a unit conversion. Conversion factors come from official international standards bodies wherever possible: the International Bureau of Weights and Measures (BIPM), the US National Institute of Standards and Technology (NIST), and the 1959 international yard and pound agreement. For special cases like temperature (which requires a shift, not just a scale) and fuel economy (where MPG and L/100km are inversely related), the converter applies the correct formula automatically.
We use officially defined conversion factors wherever possible. For example, 1 inch is defined as exactly 2.54 centimeters by international agreement since 1959. 1 pound is exactly 453.59237 grams. 1 US gallon is exactly 3.785411784 liters. Results are displayed to up to 6 significant figures, which is more than sufficient for everyday use. In the rare cases where an exact definition does not exist and a rounded factor is used, we document the precision on the relevant page.
The site includes 14 full category converters that let you switch between any pair of units within a category. It also includes 16 dedicated pair-converter pages for the most common conversions — inches to cm, kg to lbs, miles to km, Fahrenheit to Celsius, and more — each with detailed explanation of the formula, worked real-world examples, and a quick reference table. All pages are optimized for mobile use so you can convert on the go from any device without needing an app.
We take your privacy seriously. Since all conversions happen client-side, your values never leave your device. We use Google AdSense for advertising, which may use cookies, and Google Analytics to understand aggregate site usage — neither service receives your conversion values. No account is required, and we store nothing about your usage beyond your dark mode preference in browser local storage. See our Privacy Policy for details.