Unit Converter
7 categories · Metric & Imperial
Enter a value and select units to convert.
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converted value
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Unit Conversion Reference
This converter covers all major unit categories using official conversion factors from the International System of Units (SI) and NIST. All seven categories are handled in a single interface — no need to switch between separate pages.
Key conversion facts: 1 inch = 2.54 cm exactly · 1 pound = 0.453592 kg · 1 US gallon = 3.78541 liters · 0°C = 32°F · 1 mile = 1.60934 km · 1 acre = 4,046.86 m².
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Unit Conversion Questions
How many centimeters are in an inch?+
One inch equals exactly 2.54 centimeters, by international definition since 1959. This means: 1 foot = 30.48 cm, 1 yard = 91.44 cm, 1 meter = 39.3701 inches. To convert inches to centimeters, multiply by 2.54. To convert centimeters to inches, divide by 2.54.
How do I convert Celsius to Fahrenheit?+
Multiply the Celsius value by 9, divide by 5, then add 32. Formula: °F = (°C × 9/5) + 32. Example: 20°C = (20 × 9/5) + 32 = 68°F. To go the other way: °C = (°F − 32) × 5/9. Kelvin = Celsius + 273.15.
How many kilograms are in a pound?+
One pound equals exactly 0.45359237 kilograms. Conversely, one kilogram = 2.20462 pounds. One stone = 14 pounds = 6.35 kg. One ounce = 28.3495 grams. These are exact values defined by international agreement in 1959.
How many liters are in a US gallon?+
One US gallon = 3.78541 liters. The UK imperial gallon is larger: 4.54609 liters. Other key volume conversions: 1 liter = 4.22675 US cups = 33.814 US fl oz = 1,000 ml. 1 US cup = 236.588 ml. Always check whether "gallon" means US or UK.
How many miles per hour is 100 kilometers per hour?+
100 km/h = 62.137 mph. The conversion factor is: 1 km/h = 0.621371 mph. To go the other way: 1 mph = 1.60934 km/h. Other speed conversions: 1 m/s = 3.6 km/h = 2.237 mph. 1 knot = 1.852 km/h = 1.151 mph.
How many square feet are in an acre?+
One acre = 43,560 square feet = 4,046.86 square meters = 0.4047 hectares. One hectare = 2.471 acres = 10,000 m². One square mile = 640 acres. These area conversions are used in real estate, land surveying, agriculture and urban planning.
What is the difference between metric and imperial units?+
The metric system (SI) uses base units of meters, kilograms and liters, with decimal multipliers (kilo=1000, milli=0.001). It is used by every country except the US, Myanmar and Liberia for everyday measurement. The imperial system uses inches, pounds and gallons with irregular conversion factors. The US uses a variation called US customary units, which differs slightly from UK imperial (e.g., US gallon ≠ UK gallon).
How many megabytes are in a gigabyte?+
In the decimal (SI) system: 1 GB = 1,000 MB = 1,000,000 KB. In the binary system used by operating systems: 1 GiB = 1,024 MiB. This difference explains why a "1 TB" hard drive shows as 931 GB in Windows. This converter uses the SI decimal system (powers of 1,000).
How do I convert miles to kilometers?+
Multiply miles by 1.60934 to get kilometers. Example: 5 miles = 8.047 km. 26.2 miles (marathon) = 42.195 km. To go the other way, divide by 1.60934 (or multiply by 0.62137). The exact SI definition: 1 international mile = 1,609.344 meters.
What is absolute zero in Celsius and Fahrenheit?+
Absolute zero is the lowest possible temperature, where all molecular motion stops. It equals 0 Kelvin = −273.15°C = −459.67°F. The Kelvin scale starts at absolute zero, making it essential for scientific calculations. Room temperature is approximately 293 K = 20°C = 68°F.