Free Unit Converter
Convert between length, weight, temperature, volume, area, speed, and digital data units. Type in either field and see the result instantly.
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Frequently Asked Questions
How many centimeters are in an inch?+
1 inch = 2.54 centimeters exactly. This is the official definition of the international inch. So 1 cm ≈ 0.3937 inches.
How do I convert Celsius to Fahrenheit?+
Use the formula: °F = (°C × 9/5) + 32. For example, 100°C = (100 × 1.8) + 32 = 212°F. To go the other way: °C = (°F − 32) × 5/9.
How many pounds in a kilogram?+
1 kilogram = 2.20462 pounds. So to convert kg to lbs, multiply by 2.20462. To convert lbs to kg, divide by 2.20462 (or multiply by 0.453592).
How many feet in a meter?+
1 meter = 3.28084 feet. Equivalently, 1 foot = 0.3048 meters exactly.
What is the difference between KB and KiB?+
KB (kilobyte) in the SI standard = 1,000 bytes. KiB (kibibyte) = 1,024 bytes. This tool uses the binary convention (1 KB = 1,024 bytes) which is how operating systems report file sizes. Hard drive manufacturers use the decimal convention (1 KB = 1,000 bytes), which is why your 1 TB drive shows as ~931 GB in Windows.
How do I convert miles to kilometers?+
1 mile = 1.60934 kilometers. Multiply miles by 1.60934 to get km. A useful approximation: multiply by 1.6 and add 0.6% for a close enough answer in everyday use.
How many ounces in a pound?+
There are 16 avoirdupois ounces in a pound (the standard weight ounce used in the US). There are also troy ounces (used for precious metals) where 1 troy pound = 12 troy ounces. This converter uses standard (avoirdupois) ounces.
Metric vs. Imperial: Why the World Uses Two Systems
The metric system (SI) is used by almost every country in the world for science, medicine, and everyday life. The United States, Liberia, and Myanmar are the only countries that have not fully adopted the metric system, which is why American professionals frequently need to convert between the two. The metric system is built on powers of 10 — 1 meter = 100 centimeters = 1000 millimeters — making arithmetic between units trivially simple. Imperial units have no such regularity: 1 mile = 5,280 feet = 63,360 inches.
Length conversions: the ones you actually need
The most common length conversions in everyday use: 1 inch = 2.54 cm (exact, by international agreement since 1959). 1 foot = 30.48 cm. 1 mile = 1.609 km. A useful approximation for km to miles: multiply by 0.6 (exact: multiply by 0.621). For height, 5 feet = 152.4 cm, 6 feet = 182.9 cm. In engineering and construction, you frequently encounter both millimeters (for precision manufacturing) and inches (for American lumber dimensions and HVAC specifications).
Temperature conversions: Celsius, Fahrenheit, Kelvin
The Celsius scale is based on water: 0°C = freezing, 100°C = boiling (at sea level). Fahrenheit uses different reference points — 32°F = freezing, 212°F = boiling. A useful mental shortcut: to convert Celsius to Fahrenheit, double it and add 30 (not exact, but close enough for quick estimates). The exact formula is °F = (°C × 9/5) + 32. Kelvin is used in physics and chemistry — it starts at absolute zero (−273.15°C), making all values positive and allowing direct ratio comparisons. 0 Kelvin is the coldest temperature physically possible; room temperature is approximately 293–298 K.
Digital data: why your 1 TB drive shows as 931 GB
Hard drive manufacturers use the decimal definition (1 TB = 1,000,000,000,000 bytes). Operating systems (Windows, macOS, Linux) use the binary definition (1 TiB = 1,099,511,627,776 bytes). A "1 TB" drive contains exactly 1,000,000,000,000 bytes. When Windows divides that by 1,073,741,824 (1 binary GB), it gets approximately 931 GB. This is not a scam — it is a definition disagreement. This converter uses binary definitions (1 KB = 1,024 bytes), matching how operating systems report sizes. For network speeds (Mbps, Gbps), ISPs use decimal (1 Mbps = 1,000,000 bits), which is why your 100 Mbps internet connection downloads at ~12 MB/s (100,000,000 ÷ 8 ÷ 1,024,000 ≈ 11.9 MB/s).
Weight vs. mass: a common confusion
Strictly speaking, kilograms measure mass (the amount of matter), while Newtons measure weight (the force of gravity on that mass). In everyday usage, "weight" and "mass" are used interchangeably because we all live in approximately the same gravitational field. The pound (lb) is technically a unit of force (weight) in the imperial system, but the pound-mass (lbm) is used for the same purpose as kilograms in everyday contexts. For business applications like shipping, see the Profit Margin Calculator for cost calculations.