Unit Converter
Convert between different units of measurement
Quick Reference
Why Unit Conversion Matters
The world uses multiple measurement systems — primarily the International System of Units (SI/metric) used by most of the world and US customary units (feet, pounds, gallons, Fahrenheit) used primarily in the United States. Understanding how to convert between these systems is essential for science, engineering, cooking, travel, international shopping, and everyday life. This converter handles the most commonly needed categories instantly and accurately.
Common Conversions You Should Know
- Length: 1 inch = 2.54 cm, 1 foot = 30.48 cm, 1 mile = 1.609 km, 1 meter = 3.281 feet
- Weight: 1 pound = 0.454 kg, 1 kg = 2.205 lbs, 1 ounce = 28.35 grams, 1 stone = 14 pounds = 6.35 kg
- Volume: 1 gallon (US) = 3.785 liters, 1 cup = 236.6 mL, 1 pint = 473 mL, 1 liter = 33.8 fluid ounces
- Area: 1 acre = 4,047 m², 1 hectare = 2.47 acres, 1 sq ft = 0.093 m², 1 sq mile = 640 acres
- Speed: 1 mph = 1.609 km/h, 1 m/s = 3.6 km/h, 1 knot = 1.852 km/h (nautical)
Temperature: A Special Case
Temperature conversion requires formulas rather than simple multiplication, because the scales have different zero points. The three major temperature scales are:
- Celsius (°C): Water freezes at 0°C, boils at 100°C. Used by most of the world for weather and cooking.
- Fahrenheit (°F): Water freezes at 32°F, boils at 212°F. Used in the US for weather and cooking.
- Kelvin (K): Absolute scale where 0K = absolute zero (no thermal energy). Used in science. No degree symbol — K, not °K. 0K = -273.15°C.
Key conversions: °F = (°C × 9/5) + 32 | °C = (°F − 32) × 5/9 | K = °C + 273.15. Quick reference: 20°C = 68°F (room temperature), 37°C = 98.6°F (body temperature), 100°C = 212°F (boiling water).
The Metric System: Why It's Simpler
The SI/metric system is built on powers of 10, making mental math and conversion between related units extremely simple. The core prefixes you need to know: milli- (÷1000), centi- (÷100), kilo- (×1000), mega- (×1,000,000). So: 1 kilometer = 1,000 meters = 100,000 centimeters = 1,000,000 millimeters. Compare that to US customary where 1 mile = 5,280 feet = 63,360 inches — memorization required!