Unit Converter
Convert length, weight, temperature, speed and more
How to use Unit Converter
Convert length, weight, temperature, speed, area and volume units. 100+ units supported. Free online unit converter tool.
When do you need a unit converter?
Unit conversion is a constant need across science, cooking, travel, construction, and everyday life. The metric and imperial systems coexist globally — the US primarily uses imperial, while most other countries use metric, creating conversion needs at every international interaction.
- Cooking and recipes: US recipes use cups, ounces, and Fahrenheit. European recipes use grams, milliliters, and Celsius. Convert to your local system before cooking to avoid measurement errors.
- Travel: Speed limits in km/h vs mph (UK and USA still use mph), fuel prices per liter vs gallon, distances in km vs miles — all require conversion when crossing borders.
- Construction and DIY: Building materials are sold in different units depending on the country. Convert lumber dimensions, paint coverage area, and pipe diameters between metric and imperial.
- Science and engineering: Convert between SI units and other measurement systems for cross-disciplinary work or equipment specifications from different countries.
- E-commerce: Product dimensions and weights in international shipping — convert to understand if a product fits your space or meets carrier weight limits.
SI prefixes: kilo (×1,000), mega (×1,000,000), milli (÷1,000), micro (÷1,000,000), nano (÷1,000,000,000). These prefixes apply to any base SI unit: kilogram, kilometer, millisecond, micrometer.
Frequently Asked Questions
Why does the US still use imperial units?
The US attempted to transition to metric in the 1970s with the Metric Conversion Act (1975) but the process was voluntary and never completed. Industry, education, and infrastructure remained largely imperial. The UK made a similar partial transition — metric for most purposes but miles for roads, pints for beer. Changing deeply embedded measurement systems in a large economy is politically and practically difficult.
What is the difference between mass and weight?
Mass is the amount of matter in an object — measured in kilograms, grams, or pounds (as mass). Weight is the gravitational force on that mass — measured in Newtons. On Earth, the distinction rarely matters practically: a 1kg mass weighs approximately 9.8 Newtons. On the Moon, the same mass weighs about 1.6 Newtons. In everyday usage, 'weight' commonly refers to mass.
What is the difference between fluid ounces and weight ounces?
A fluid ounce (fl oz) measures volume — approximately 29.57ml (US) or 28.41ml (UK). A weight ounce measures mass — approximately 28.35g. They are different units that happen to share the name 'ounce'. Water is roughly 1:1 (1 fl oz of water weighs about 1 oz), but other liquids differ significantly.
What is the difference between US and UK measurement systems?
The US and UK systems mostly share names but differ in values. UK (Imperial) gallon = 4.546 liters. US gallon = 3.785 liters. UK pint = 568ml; US pint = 473ml. UK ton (long ton) = 1,016kg; US ton (short ton) = 907kg. Always specify US or UK when converting volumes and large masses.
How do I convert between Celsius and Fahrenheit mentally?
Quick approximation: double the Celsius and add 30 (accurate to ±2°F for most everyday temperatures). Exact formula: F = C × 9/5 + 32. Common reference points: 0°C = 32°F (freezing), 20°C = 68°F (room temperature), 37°C = 98.6°F (body temperature), 100°C = 212°F (boiling).
Metric vs imperial vs US customary
The metric (SI) system is used by 95% of the world — base-10 units, easy conversion between prefixes. Imperial (UK-origin) uses inconsistent conversion factors: 12 inches per foot, 3 feet per yard, 1,760 yards per mile. US customary is similar to Imperial but with different values for volume (US gallon ≠ Imperial gallon). The metric system is unambiguously superior for scientific and mathematical work. Imperial persists through cultural inertia in the US and partially in the UK.