Unit Converter — Length, Weight, Temperature & More

The International System of Units (SI) is the modern form of the metric system and is the world's most widely used measurement standard, adopted officially by nearly every country. SI is built on base units — metre (length), kilogram (mass), second (time), kelvin (temperature) — and uses decimal prefixes (kilo = ×1000, centi = ÷100, milli = ÷1000) to express larger or smaller quantities. This makes conversions within the metric system straightforward: 1 kilometre = 1000 metres, 1 kilogram = 1000 grams. Scientists, engineers, and most international industries use SI exclusively. When working with data storage, the SI prefixes kilobyte (KB = 1000 bytes) and kibibyte (KiB = 1024 bytes) differ — an important distinction in computing contexts that this tool handles correctly.

The imperial system, used primarily in the United States and partially in the United Kingdom, uses different base units: feet and miles for length, pounds and ounces for weight, Fahrenheit for temperature, and gallons for volume. US customary units often differ subtly from UK imperial units — for example, a US gallon (3.785 L) is smaller than a UK gallon (4.546 L), and US fluid ounces differ from UK fluid ounces. These inconsistencies can cause significant errors in recipes, engineering, and manufacturing if not properly accounted for. Converting between imperial and SI requires fixed conversion factors: 1 inch = 2.54 cm exactly, 1 pound = 0.4536 kg, and 1 mile = 1.609344 km. This tool handles all these conversions using precise factors.

Temperature is the one measurement category where unit conversion cannot be done by simple multiplication. Celsius and Fahrenheit scales have different zero points: 0°C is the freezing point of water, while 0°F is a different reference entirely. The correct formula from Celsius to Fahrenheit is (°C × 9/5) + 32, and from Fahrenheit to Celsius is (°F − 32) × 5/9. Kelvin, the SI base unit of temperature, uses absolute zero as its starting point — K = °C + 273.15. This means that "doubling the temperature" has different meanings in different scales: 20°C doubled is 40°C, but converting to Fahrenheit (68°F vs. 104°F) shows the ratio is not 2:1. This converter applies the correct formulas automatically for all temperature conversions.

For length, the most common conversions are: 1 inch = 2.54 cm, 1 foot = 30.48 cm, 1 yard = 91.44 cm, 1 mile = 1.609 km, and 1 nautical mile = 1.852 km. For weight, key conversions are: 1 pound = 453.6 g, 1 ounce = 28.35 g, and 1 stone (UK) = 6.35 kg. For volume, 1 US cup = 236.6 mL, 1 US fluid ounce = 29.57 mL, 1 US gallon = 3.785 L, and 1 litre = 1.0567 US quarts. For speed, 1 mph = 1.609 km/h and 1 knot = 1.852 km/h. Using the swap button in the converter lets you instantly reverse any conversion — if you find 5 km in miles, one click gives you miles to km.

Digital storage units are a frequent source of confusion because manufacturers and operating systems use different conventions. Hard drive manufacturers typically use SI prefixes (1 GB = 1,000,000,000 bytes), while operating systems traditionally used binary prefixes (1 GiB = 1,073,741,824 bytes). This is why a "500 GB" drive appears as roughly 465 GB in Windows. The IEC introduced explicit binary prefixes in 1998 — kibibyte (KiB), mebibyte (MiB), gibibyte (GiB), tebibyte (TiB) — to eliminate this ambiguity. This converter supports both SI and binary storage units, so you can accurately compare advertised drive capacities with what your OS reports, or calculate precise storage requirements for software engineering and system administration tasks.