Unit Converter Online Free — Length, Weight, Temperature & More
Convert between more than 100 units across 12 measurement categories. Supports length, weight/mass, temperature, area, volume, speed, time, digital storage, energy, pressure, angle, and fuel economy. Conversion is instant with a multi-unit panel that shows all equivalent values simultaneously. Includes a 10-item history for quick recall. All calculations run in your browser.
100% private. All conversions are calculated locally using official SI conversion factors. No data is sent to any server.
How to Convert Units Online Free
- 01
Select a category
Click any of the 12 category buttons: Length, Weight, Temperature, Area, Volume, Speed, Time, Storage, Energy, Pressure, Angle, or Fuel Economy.
- 02
Choose units and enter a value
Select the From and To units from the dropdowns. Type a number — conversion happens instantly. Use the swap button to reverse direction.
- 03
View all conversions at once
The multi-conversion panel below shows the value in every unit in the category. Click any row to set it as your target unit.
Frequently Asked Questions
How accurate are the unit conversions?
The conversions use the official SI-defined conversion factors with full IEEE 754 double-precision floating point accuracy (15–17 significant digits). For example, 1 inch is exactly 0.0254 meters by definition. Temperature formulas (Celsius ↔ Fahrenheit ↔ Kelvin ↔ Rankine) use the exact standard formulas. Results are displayed to up to 10 significant figures.
How do I convert temperature between Celsius and Fahrenheit?
Select the "Temperature" category, choose Celsius as the From unit and Fahrenheit as the To unit, then enter your value. For example, 100°C converts to 212°F using the formula °F = (°C × 9/5) + 32. The multi-unit panel simultaneously shows the result in all four temperature units: Celsius, Fahrenheit, Kelvin, and Rankine.
What is the difference between MB and MiB?
MB (Megabyte) uses the decimal system: 1 MB = 1,000,000 bytes (10⁶). MiB (Mebibyte) uses the binary system: 1 MiB = 1,048,576 bytes (2²⁰). Hard drive manufacturers use MB (decimal), while operating systems historically reported storage in MiB (binary). This tool supports both decimal (KB/MB/GB/TB) and binary (KiB/MiB/GiB/TiB) units.
How do I convert miles to kilometers?
Select the "Length" category. Choose "Mile" from the From dropdown and "Kilometer" from the To dropdown. Enter the number of miles. 1 mile = 1.60934 km exactly (by definition, 1 international mile = 1,609.344 meters). The result updates instantly as you type.
Can I convert multiple units at the same time?
Yes. After entering a value, the "All [category] conversions" panel shows the equivalent in every unit in the category simultaneously. Click any row to set it as your To unit in the main converter. This is useful for quick comparison — for example, seeing 1 meter expressed in all length units at once.