Best Free Online Developer Tools to Use in 2026
A practical, opinionated list of the best free online developer tools worth using in 2026, organized by category so you can find what you need fast.
Aug 08, 2026
Unit Converter
Convert between units of length, mass, volume, temperature, data, speed, time, area, pressure, energy, and frequency.
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What Is a Unit Converter?
A unit converter is a tool that translates a quantity expressed in one unit to its equivalent in another unit within the same measurement category. For example, converting 5 miles to kilometers or 100°F to Celsius.
Unit conversion is essential in science, engineering, cooking, travel, and everyday life. This tool supports 11 categories with over 80 units and uses standard conversion factors defined by international agreements (SI, NIST).
Conversions are performed by multiplying by a conversion factor relative to a base unit. Temperature is the exception — it requires both scaling and offset adjustments (e.g., °C to °F uses the formula F = C × 9/5 + 32).
How to Use
- Select a category — Choose from 11 categories: Length, Mass, Volume, Temperature, Data Size, Speed, Time, Area, Pressure, Energy, or Frequency.
- Enter a value — Type the number in the "From" input field. The conversion updates in real-time as you type.
- Choose units — Select the source unit and target unit from the dropdowns. Use the Swap button to reverse them.
- View the conversion table — The full table below shows the entered value converted to every unit in the selected category.
Supported Categories
Length
Meter, kilometer, centimeter, millimeter, mile, yard, foot, inch, nautical mile
Mass
Kilogram, gram, milligram, tonne, pound, ounce, stone, US/UK ton
Volume
Liter, milliliter, cubic meter, gallon (US/UK), quart, pint, cup, fluid ounce, tablespoon, teaspoon, cubic foot
Temperature
Celsius, Fahrenheit, Kelvin, Rankine, Réaumur
Data Size
Bit, byte, kilobyte, megabyte, gigabyte, terabyte, petabyte, kibibyte, mebibyte, gibibyte, tebibyte, pebibyte
Speed
Meter/second, kilometer/hour, mile/hour, knot, foot/second, Mach, speed of light
Time
Second, millisecond, microsecond, nanosecond, minute, hour, day, week, month, year
Area
Square meter, square kilometer, square mile, square foot, square inch, acre, hectare
Pressure
Pascal, kilopascal, megapascal, bar, millibar, atmosphere, PSI, mmHg, torr, inch Hg, hectopascal
Energy
Joule, kilojoule, calorie, kilocalorie, watt-hour, kilowatt-hour, BTU, foot-pound, erg, electronvolt
Frequency
Hertz, kilohertz, megahertz, gigahertz, terahertz, RPM, BPM, degree/second, radian/second
Frequently Asked Questions
How accurate are the conversions?
All conversion factors follow international standards (SI base units, NIST definitions). Results are displayed with up to 10 decimal places of precision. Very large or very small values use scientific notation.
Why does temperature use a different formula?
Temperature scales have different zero points (offsets) in addition to different unit sizes. For example, 0°C = 32°F = 273.15 K. This requires an offset adjustment, not just multiplication. The conversion table handles this automatically.
What is the difference between MB and MiB?
MB (megabyte) uses decimal prefixes: 1 MB = 1,000,000 bytes. MiB (mebibyte) uses binary prefixes: 1 MiB = 1,048,576 bytes (2⁻⁵). Hard drive manufacturers typically use decimal units, while operating systems often report in binary units.
Is this tool client-side?
Yes, 100%. All conversion logic runs in your browser using JavaScript. No data is sent to any server. The tool works offline after the page has loaded.
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