Unit Converter
Convert length, weight, temperature, volume, area, and speed between metric and imperial units — fast and precise.
How to use this converter
Pick a category (length, weight, temperature, volume, area, or speed), enter a value, choose source and target units. The result updates instantly. Use the swap button (⇄) to flip the direction.
Metric vs imperial, briefly
The metric system (used in nearly every country except the US, Liberia, and Myanmar) uses base-10 scaling: 1,000 grams = 1 kilogram, 1,000 meters = 1 kilometer. This makes mental math easy. Imperial and US customary units (inches, feet, miles, pounds, gallons) have historical roots and irregular ratios — 12 inches per foot, 5,280 feet per mile, 16 ounces per pound. No way around the awkwardness; the converter does the work for you.
Common everyday conversions
Cooking: 1 cup = 240 mL (approx); 1 tablespoon = 15 mL; 1 teaspoon = 5 mL. Travel: 100 km/h ≈ 62 mph; 100 km ≈ 62 miles. Body weight: 1 kg = 2.205 lb (easy rule: double it and add 10%). Height: 1 inch = 2.54 cm; 6 feet ≈ 183 cm. Temperature: 20°C = 68°F (a nice room temperature); 100°F ≈ 37.8°C (hot summer day).
Why US gallons are different from UK gallons
The US gallon (3.785 L) was standardized from the older English wine gallon. The UK imperial gallon (4.546 L) was later defined (1824) based on the volume of 10 lb of water at 62°F. They're genuinely different units. This calculator uses US customary volumes by default — if you need imperial, multiply US gallons by 0.8327 to get imperial gallons.
Temperature: the tricky conversion
Unlike length or weight, temperature scales don't share a zero point. 0°C is the freezing point of water; 0°F is about -17.8°C (historically set to the lowest temperature a Danish chemist could reproduce in the 1720s using a salt-ice brine). Kelvin uses absolute zero (-273.15°C) as its origin. That's why temperature conversions use addition/subtraction as well as scaling.
Frequently asked questions
Are these US or imperial gallons?▾
This calculator uses US customary units by default (US gallons, US quarts, US cups, etc.), which is what most users expect. A US gallon is 3.785 liters; an imperial (UK) gallon is 4.546 liters — they are NOT the same. If you need imperial-gallon precision, use a factor of 4.546 L/gal manually.
Why do I see rounding on large or tiny values?▾
The converter preserves up to 6 significant digits for display. If you need more precision (scientific, engineering, cooking), the raw computation is accurate to JavaScript's double-precision floating point (about 15-17 digits). For most everyday use, 6 digits is far more than needed.
How are temperatures converted?▾
Temperature conversions aren't linear scaling — Celsius and Fahrenheit have different zero points, and Kelvin has a different zero point still (absolute zero). Formulas: °F = °C × 9/5 + 32; K = °C + 273.15. The calculator handles all combinations directly.
Can I convert between metric and imperial in one step?▾
Yes — pick any source unit and any target unit within the same category. Examples: meters to feet, kilograms to pounds, liters to gallons. Just change the category if you need a different dimension (length vs weight vs volume etc).
Related calculators
Tip Calculator
Calculate the tip and split the bill. Works for any currency — choose a tip percent, number of people, and whether to round up.
Age Calculator
Calculate exact age in years, months, days, weeks, hours, and minutes. Also shows days until your next birthday.
Compound Interest Calculator
See how compound interest grows your money over time. Compare daily, monthly, quarterly, and annual compounding with regular contributions.