SumUnit Converter
Convert length, weight, temperature and volume between metric and US units — instantly, with the exact formula shown so you can see how the answer was calculated.
Result
How It Works
Most unit conversions are simple multiplications. Every unit in a category is defined by its size relative to one base unit — meters for length, kilograms for weight, liters for volume. To convert, the value is first turned into the base unit and then into the target unit. For example, 1 inch is exactly 0.0254 meters and 1 centimeter is 0.01 meters, so 1 centimeter equals 0.01 ÷ 0.0254 = 0.3937 inches. That is why 100 cm converts to 39.37 inches: 100 × 0.3937 = 39.37.
Temperature is the exception, because its scales have different zero points as well as different step sizes. Fahrenheit and Celsius are linked by two formulas: °F = °C × 9/5 + 32, and °C = (°F − 32) × 5/9. Kelvin uses the same step size as Celsius but starts at absolute zero, so K = °C + 273.15. That is why 32°F is exactly 0°C (the freezing point of water) and 212°F is exactly 100°C (the boiling point at sea level).
Volume units here are US customary measures — the cup, pint, quart and gallon you will find on American recipes and fuel pumps. One US gallon is 3.785 liters, and each step down halves the size: 1 gallon = 4 quarts = 8 pints = 16 cups. Weight uses the US short ton (2,000 lb, or 907.18 kg), not the metric tonne (1,000 kg). Worked examples: 1 kilogram = 2.2046 pounds, 1 US gallon = 3.7854 liters, and 68°F = 20°C, a comfortable room temperature.
Frequently Asked Questions
How accurate are the conversions?
They use exact, internationally defined conversion factors (for example, 1 inch = 2.54 cm exactly, and 1 pound = 0.45359237 kg exactly). Results are rounded to 4 decimal places for display, which is more precision than everyday cooking, travel or DIY needs.
Why is temperature conversion different?
Length, weight and volume scales all start at zero, so converting is just multiplication. Temperature scales start at different points — 0°F is not the same temperature as 0°C — so the formula needs an offset (+32, or +273.15 for Kelvin) as well as a multiplier.
Is this the US gallon or the UK gallon?
The US gallon (3.785 liters), along with US cups, pints and quarts. The UK (imperial) gallon is larger at 4.546 liters, so check which one a recipe or manual means before converting.
What is the difference between a ton and a tonne?
The US short ton is 2,000 pounds (907.18 kg). The metric tonne is 1,000 kg (2,204.6 lb). This converter's "Ton (US)" is the short ton used in the United States.
Can I convert negative values?
Yes for temperature — negative Celsius and Fahrenheit values are perfectly valid. Length, weight and volume accept negative numbers too, though a negative distance or weight has no physical meaning in most cases.
Last updated: November 2026