Free Online Unit Converter

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Metric vs Imperial: Why Conversions Matter

Most of the world uses the International System of Units (SI), commonly known as the metric system. The United States, Liberia, and Myanmar are the only countries that have not officially adopted SI as their primary system, still using the imperial (US customary) system for everyday measurements. The United Kingdom uses a mix — metric for most purposes but miles for road distances and pints for draught beer.

For anyone working across borders — ordering products internationally, following a recipe from another country, understanding a foreign news report, or setting up international shipping — quick unit conversions are a daily necessity.

Common Conversions at a Glance

Category	Common conversion	Result
Length	1 kilometre	≈ 0.621 miles
Length	1 mile	≈ 1.609 kilometres
Length	1 foot	≈ 30.48 centimetres
Length	1 inch	≈ 2.54 centimetres
Weight	1 kilogram	≈ 2.205 pounds
Weight	1 pound	≈ 453.6 grams
Temperature	0 °C	≈ 32 °F (freezing)
Temperature	100 °C	≈ 212 °F (boiling)
Temperature	37 °C	≈ 98.6 °F (body temp)
Volume	1 litre	≈ 0.264 US gallons
Speed	100 km/h	≈ 62.1 mph
Data	1 GB	≈ 0.931 GiB (binary)

Temperature: The Exception to the Rule

Most unit conversions are simple multiplication by a fixed factor. Temperature is different because Celsius and Fahrenheit have different zero points. The formulas are:

°F = (°C × 9/5) + 32
°C = (°F − 32) × 5/9
K = °C + 273.15 — Kelvin has no negative values; 0 K is absolute zero

A quick mental trick: for a rough Fahrenheit-to-Celsius conversion, subtract 30 and halve the result. For example, 70 °F → (70−30)/2 = 20 °C. The actual answer is 21.1 °C, but the estimate is usually close enough for everyday use.

How to Use Unit Converter

1

Select a unit category

Pick a category from the tabs: Length, Weight, Temperature, Volume, Area, Speed, or Data. The relevant units appear below.
2

Type a value

Click any unit field and type your value. All other units in the same category update instantly with the converted values.
3

Copy any result

Click the copy icon next to any converted value to copy it to your clipboard for use in documents, spreadsheets, or emails.

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Frequently Asked Questions

All conversions use the exact SI-defined values where available. For example, 1 inch = 25.4 mm exactly (by definition), 1 mile = 1609.344 m exactly, and 1 pound = 0.45359237 kg exactly. Temperature conversions use the exact formulas: °C = (°F − 32) × 5/9 and K = °C + 273.15. Results are displayed to up to 10 significant figures.

KB (Kilobyte) = 1,000 bytes (SI standard, used by hard drive manufacturers and most file transfer contexts). KiB (Kibibyte) = 1,024 bytes (IEC standard, used by operating systems to report RAM and file sizes). This discrepancy is why a "1 TB" hard drive shows ~931 GB in Windows — the drive is 1,000,000,000,000 bytes, but Windows reports in GiB.

A nautical mile is defined as exactly 1,852 metres. It was originally based on one minute of arc along a meridian of the Earth. It is used in maritime and aviation navigation because it relates directly to degrees of latitude — 1 degree of latitude ≈ 60 nautical miles.

A stone is a unit of weight used mainly in the United Kingdom and Ireland, equal to exactly 14 pounds or approximately 6.35 kg. It is commonly used for measuring human body weight in those countries.

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