Unit Converter

Each unit is stored as a multiple of one base unit for its category: meters for length, kilograms for mass, liters for volume, bytes for data, seconds for time, pascals for pressure and joules for energy. A conversion multiplies your value into the base unit and divides it back out into the target, so 1 inch is always exactly 0.0254 m and 1 mile exactly 1,609.344 m, with no rounded intermediate step.

Temperature is the one category that cannot work this way, because Celsius, Fahrenheit and kelvin start counting from different zero points. Those conversions use the full formulas instead, for example °F = °C × 9/5 + 32, and the converter warns you if a value falls below absolute zero. Results are shown with up to six significant digits and your language's thousands separator; the formula line under the tool gives the precise factor when you need more.

Since the international yard and pound agreement of 1959, the inch is defined as exactly 2.54 cm and the avoirdupois pound as exactly 0.45359237 kg. Everything else in the imperial and US customary systems hangs off those two numbers: a foot is 12 inches, a mile 5,280 feet, an ounce 1/16 of a pound and a stone 14 pounds. The metric side has been anchored to physical constants since 2019, when the kilogram stopped being a metal cylinder in France and was redefined through the Planck constant.

Two traps are worth knowing. Volume units here are US customary: a US gallon is 3.785411784 L, while the British imperial gallon is 4.54609 L, about 20% larger, and a US fluid ounce (29.57 mL) is slightly bigger than an imperial one (28.41 mL). Data sizes use decimal prefixes as drive makers and network speeds do, so 1 GB is 1,000,000,000 bytes; operating systems that report in binary units (GiB, 1,073,741,824 bytes) will show a smaller number for the same disk.

Physical sizes and screen sizes only meet through resolution. A photo that must be 3.5 × 4.5 cm on paper needs a pixel size that depends on the printer's dots per inch, which is why print shops ask for 300 DPI. The pixel converter does that arithmetic for you, and resize image to cm sets the pixels and the DPI tag in one step, so a document photo comes out of the printer at the size the form asks for.

For everyday lengths, the most searched pair is centimeters to inches; for body weight and luggage it is kilograms to pounds. Each pair page has its own converter preset, two printed reference tables and the arithmetic written out step by step.