Unit Converter

Unit conversion shows up across almost every science and math class — converting a measurement in a physics problem, a recipe in a chemistry lab, or just checking whether a distance in miles matches one in kilometers. This tool covers four of the most common categories: length, weight, temperature, and volume, each with the units you're most likely to actually need.

Length, weight, and volume all convert the same way — multiplying by a fixed factor between two units of the same physical quantity, so 12 inches always converts to exactly 1 foot, no matter how many times you run it. Temperature is the one category that works differently: Celsius, Fahrenheit, and Kelvin don't share a common zero point, so converting between them uses dedicated formulas (for example, °F = °C × 9/5 + 32) rather than a simple multiplier.

Volume and weight use US customary units (US gallons, quarts, and the standard avoirdupois pound and ounce) — if you need UK/imperial equivalents, note that those use different gallon and pint sizes and won't match these numbers. For temperature, this tool won't accept a value below absolute zero (−273.15°C), since that's not physically possible regardless of which unit you enter it in.

A worked example

Converting 98.6°F (a familiar reference point for body temperature) to Celsius uses the dedicated formula rather than a multiplier: °C = (°F − 32) × 5/9 = (98.6 − 32) × 5/9 = 66.6 × 5/9 = 37.0°C exactly. Compare that to a linear conversion like length: 10 miles to kilometers simply multiplies by a fixed factor, 10 × 1.609344 = 16.09344 km — no offset or special-case formula needed, since length units share a common zero point.

A common misconception

It's natural to assume every unit conversion works the same way — multiply by a factor and you're done — but that only holds for units of the same physical quantity that share a common zero point, like length, weight, or volume. Temperature breaks this pattern: 0°F is not the same physical state as 0°C, so there's no single multiplier that converts between them, which is exactly why this calculator routes every temperature conversion through a dedicated formula instead of the multiply-by-a- factor approach used for the other three categories.

Where unit systems disagree

“Gallon” doesn't mean the same volume worldwide: a US gallon is exactly 3.785411784 liters, while a UK imperial gallon is exactly 4.54609 liters — about 20% larger. The two systems were standardized separately, and both remain in everyday use in different countries, so a recipe or a fuel-economy figure using “gallons” can mean two genuinely different volumes depending on where it was written. This calculator uses US customary units throughout for volume and weight; length units (inches, feet, yards, miles), though, are identical between the US and UK, since both countries adopted the same international definition — exactly 0.9144 meters per yard — under a 1959 agreement signed by the US, UK, Canada, Australia, New Zealand, and South Africa.

How to use your result

Match your precision to the context: a science lab result usually needs to preserve significant figures rather than a long decimal tail, while an everyday conversion (a recipe, a travel distance) is generally more useful rounded to something readable. This calculator shows up to 6 decimal places so the exact figure is always available; round it further yourself when a shorter number better fits what you're using it for.

Metric vs. imperial systems

The metric system's biggest practical advantage is that every unit within a category relates by a power of ten — 1,000 millimeters to a meter, 1,000 meters to a kilometer — so converting between them is just shifting a decimal point. Imperial and US customary units use historical, non-decimal ratios instead (12 inches to a foot, 3 feet to a yard, 16 ounces to a pound), which is exactly why this tool's conversion factors look like precise, unround numbers such as 0.3048 or 0.45359237 — they're exact by international definition, just not round in decimal terms the way metric-to-metric conversions are.