📐 Unit Converter ☆

Overview

Our Free Unit Converter is a free online conversion calculator that instantly converts between hundreds of measurement units across 12+ categories, all right in your browser. Categories include length (cm, inches, feet, meters, km, miles), weight (kg, lbs, ounces, grams), temperature (Celsius, Fahrenheit, Kelvin), volume (liters, gallons, milliliters, cups), area (sq meters, sq feet, acres, hectares), speed (km/h, mph, knots), time (seconds, minutes, hours, days, weeks, years), pressure (pascal, bar, psi), energy (joules, calories, kWh), power (watts, horsepower), angle (degrees, radians), and digital storage (bytes, KB, MB, GB, TB). Simply select your category, enter a value, choose source and target units, and the result appears instantly with scientific precision. All calculations use internationally recognized conversion factors. Perfect for students solving homework, engineers verifying measurements, travelers converting units abroad, cooks adapting recipes between metric and imperial, and anyone needing quick unit conversions. All processing happens entirely in your browser. No downloads, no sign-up, no data collection.

How unit conversion stays accurate

Every conversion is computed against a base unit per category using internationally recognized factors: 1 inch is exactly 25.4 mm, 1 pound is 0.45359237 kg, and temperature uses the offset formulas rather than simple ratios. Values are converted to the base unit and back, so any pair in a category is consistent and chain conversions do not drift. Results keep full floating-point precision and are displayed with sensible rounding, and the formula shown lets you verify the math.

How it works and what it supports

Property	Unit converter behavior
Categories	Length, weight, temperature, volume, area, speed, time, pressure, energy, power, angle, data
Units	Hundreds of metric, imperial and scientific units
Factors	Internationally recognized definitions, base-unit normalization
Temperature	Offset formulas for Celsius, Fahrenheit and Kelvin
Precision	Full floating point, rounded for display
Processing	100% client-side JavaScript, nothing transmitted
Cost	Free, no account, no ads

Privacy: conversions are private

Measurements can reveal product specs, engineering tolerances or medical values, so all math runs locally. Nothing is stored or logged, and the page works offline after loading.

Conversion tips

• Use the formula shown to double-check critical engineering values.
• Watch significant figures: converting does not add precision that was not there.
• For cooking, prefer volume for liquids and weight for dry ingredients.
• Remember US and imperial gallons differ, check the label.
• For data storage, distinguish decimal (GB) from binary (GiB) units.

Related: browse all calculators for percentages, ages, dates and BMI.

Precision, rounding and significant figures

Conversion is exact arithmetic, but the number you should report depends on the use. The definitions behind the metric system are fixed, an inch is exactly 25.4 millimetres, a pound is exactly 453.59237 grams, so the converter carries full precision and rounds only for display. Rounding too early is the classic error: converting 1.5 miles to kilometres gives 2.414, and rounding that to 2.4 before converting to metres gives 2,400 instead of 2,414. Keep the full value until the final step. Significant figures matter in science and engineering: multiplying a measurement with three significant figures by an exact conversion factor keeps three, but multiplying two measured quantities cannot create precision that was not there. Watch for two traps. First, imperial and US units differ: a US gallon is 3.785 litres while an imperial gallon is 4.546 litres, so always confirm which one a recipe or specification means. Second, decimal prefixes in computing are ambiguous: a kilobyte can mean 1,000 bytes or 1,024 bytes, and the IEC names kibibyte and mebibyte exist precisely to remove that ambiguity. Finally, temperature is an offset scale, not a ratio: 20 °C is 68 °F, but doubling 20 °C does not double the Fahrenheit value, because the zero points differ.