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UnitConversion.free is a fast, ad-supported, browser-only unit converter that covers 17 measurement dimensions: length, mass, temperature, volume, speed, area, time, pressure, energy, power, frequency, angle, digital storage, data rate, force, fuel economy, and density. Each conversion is computed from a typed unit catalog with defined base factors (not a static lookup table), so results match the precision of the underlying constants and JavaScript double-precision arithmetic. Every input runs in your browser; nothing is sent to a server.

Featured conversion examples

Tap any card to open the full calculator for that conversion, complete with formula, common-values table, and FAQ:

1 m3.28084 ft25°C77°F1 kg2.20462 lbs5 km3.10686 mi1 L0.2642 US gal60 mph96.56 km/h100 Mbps100,000 kbps3,200 MHz3.2 GHz

What kind of conversion do you need?

The fastest path depends on whether you know exactly which unit pair you want or need to browse a category.

Specific conversion in mind? Jump straight to a pair page: meters to feet, Celsius to Fahrenheit, kg to lbs, km to miles, liters to gallons, cups to mL, mph to km/h, Mbps to Kbps, MPG to L/100km, MHz to GHz, joules to BTU, and km/h to m/s. Each pair page gives the lead answer, the conversion formula, a table of common values, and a short FAQ.

Working in a measurement family? Open the dimension hub for that family. The dimension page lists every supported unit, the relationships between them, and links to the most common pair-conversions inside the family.

Measurement families covered on this site

17 dimensions, each with a dedicated hub page plus the most common unit pairs broken out for quick reference. The headline summary for each family:

  • Length: SI base meter, with metric (km, cm, mm) and US/imperial (inch, foot, yard, mile, nautical mile) units. Inch is defined as exactly 25.4 mm by the 1959 international agreement.
  • Mass: SI base kilogram. Pounds and kilograms convert exactly because 1 lb is defined as 0.45359237 kg. Includes troy ounces for precious metals.
  • Temperature: Celsius, Fahrenheit, and Kelvin. -40 is the only temperature where C and F agree numerically. Kelvin is Celsius shifted to absolute zero.
  • Volume: Liters and cubic units, US fluid measure, and imperial (UK) fluid measure. US and UK gallons differ by ~20% so the source country matters.
  • Speed: m/s, km/h, mph, knots. Knots are tied to nautical miles, which is one minute of latitude along a meridian.
  • Area: Square units plus the acre and hectare for land. 1 acre is 43,560 ft² (a historical English plowing standard).
  • Time: Seconds and its prefixed multiples (ms, μs, ns) plus minutes, hours, days, weeks, and years.
  • Pressure: Pascals, bar, atmosphere, psi, mmHg, torr. Tire pressure, weather barometric pressure, and HVAC all use different conventions.
  • Energy: Joules, kilowatt-hours, calories, BTU, electron-volts. The food calorie is 1,000 thermochemical calories (a kilocalorie).
  • Power: Watts, kilowatts, horsepower, BTU/hr. 1 mechanical horsepower equals 745.7 watts.
  • Frequency: Hertz and its prefixed multiples. CPU clocks, Wi-Fi bands, and radio bands all use Hz/kHz/MHz/GHz.
  • Angle: Degrees, radians, gradians, arcminutes, arcseconds. SI base is the radian; one full turn is 2π radians.
  • Digital storage: Bytes, kilobytes, megabytes, gigabytes, terabytes, plus the binary KiB/MiB/GiB prefixes that IEC standardized in 1998.
  • Data rate: Bits per second and bytes per second across kilo, mega, and giga scales. Network speeds are decimal (1 Mbps = 1,000,000 bits/s).
  • Force: Newtons, dynes, pound-force, kilogram-force. 1 N is the force needed to accelerate 1 kg by 1 m/s².
  • Fuel economy: MPG (US and UK) and L/100km. The two metrics are inverses, which is why one rises as the other falls.
  • Density: kg/m³, g/cm³, lb/ft³, lb/in³. Water is conveniently 1 g/cm³ at 4°C, the calibration point for the original gram definition.

How accuracy and methodology work here

Every conversion on UnitConversion.free runs through a single typed unit catalog and conversion engine. Each unit is registered with its base factor relative to the SI coherent unit for that dimension, and conversion between any two units in the same dimension is a single multiplication of input value × (source base factor / target base factor). There is no static lookup table; the same engine handles all 17 dimensions.

Accuracy is bounded by the precision of the registered base factors and by JavaScript double-precision arithmetic (IEEE 754 binary64, about 15-17 significant decimal digits). For exact conversions defined by international agreement (1 ft = 0.3048 m, 1 lb = 0.45359237 kg, 1 inch = 25.4 mm, 1 mile = 1.609344 km, 1 BTU IT = 1,055.05585262 J), the factors are stored to full definitional precision. For safety-critical, legal, or regulated work, cross-reference the final result against the primary standard (NIST SP 811 for US practice, the BIPM SI brochure for international SI).

Privacy is straightforward: every conversion runs entirely in your browser. The site stores only your theme preference (light, dark, or system) in local storage so the choice persists across reloads. No conversion inputs, results, or browsing history are sent to a server.

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