Unit Converters
Free online unit conversion tools. Fast, accurate, no signup required.
Length
Meters, kilometers, miles, feet, inches and more
Weight
Kilograms, pounds, ounces, stones and more
Temperature
Celsius, Fahrenheit, Kelvin
Data Size
Bytes, KB, MB, GB, TB, PB
Speed
m/s, km/h, mph, knots
Area
Square meters, acres, hectares and more
Volume
Liters, gallons, cups and more
Unit Converters — FAQ
How accurate are the unit conversions?
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All conversions use exact or high-precision conversion factors defined by international standards bodies such as NIST and the BIPM. Results are calculated with floating-point arithmetic and displayed to up to 10 significant figures to minimize rounding errors.
Do I need to create an account to use these tools?
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No. All unit converters on FreeBoxTool are completely free and require no account, registration, or login. Simply select a category, enter your value, and get instant results.
Can I use these converters on my phone?
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Yes. All converters are fully responsive and work on any device including smartphones, tablets, and desktop computers. No app download is required — everything runs in your web browser.
Which unit systems are supported?
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The converters support the International System of Units (SI/metric), the US customary system, and the imperial system, plus specialized units such as nautical miles, knots, and data units. You can convert freely between any supported units within a category.
Where do the conversion factors come from?
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Conversion factors are sourced from definitions published by the International Bureau of Weights and Measures (BIPM) and the US National Institute of Standards and Technology (NIST). Key values such as the inch-to-centimeter ratio (2.54 exactly) are international treaty definitions.