OptiDrop

Unit Converter Online — Length, Weight, Temperature, Speed

Convert between units instantly — kilometers to miles, kg to pounds, Celsius to Fahrenheit, and more. Free online unit converter with swap button. No upload, no sign-up — 100% private.

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Free Unit Converter — Convert Length, Weight, Temperature, Speed Online

OptiDrop's Unit Converter is a free online tool that instantly converts between different units of measurement. Whether you need to convert kilometers to miles, kilograms to pounds, Celsius to Fahrenheit, or km/h to mph, this tool handles it all. Simply select a category, choose your input and output units, enter a value, and see the result instantly. The swap button lets you reverse the conversion direction with one click.

Four Conversion Categories

The converter supports four common categories. Length conversions include kilometers, meters, centimeters, miles, feet, and inches. Weight conversions cover kilograms, grams, pounds, and ounces. Temperature conversions handle Celsius, Fahrenheit, and Kelvin. Speed conversions support km/h, mph, and m/s. Each category provides all the commonly needed unit pairs for everyday use.

Instant and Private

All conversions happen instantly in your browser using standard conversion formulas. No data is uploaded to any server — enter any value with confidence that your calculations remain completely private. The tool works offline once loaded, making it reliable anywhere you have a browser.

Frequently Asked Questions

To convert kilometers to miles, multiply the distance in km by 0.621371. For example, 10 km x 0.621371 = 6.21371 miles. This converter does the calculation instantly — select Length, choose km as the input unit and miles as the output unit, then enter your value.
There are approximately 2.20462 pounds in 1 kilogram. To convert kg to pounds, multiply the weight in kg by 2.20462. To convert pounds to kg, multiply by 0.453592. This converter handles both directions automatically.
To convert Celsius to Fahrenheit, multiply the temperature by 1.8 (or 9/5) and then add 32. For example, 100 C x 1.8 + 32 = 212 F. To convert Fahrenheit to Celsius, subtract 32 and then multiply by 5/9.
Most unit conversions use a simple multiplication factor. You multiply the input value by a conversion factor to get the output. For example, 1 km = 1000 meters (factor: 1000), 1 mile = 1.60934 km (factor: 1.60934). Temperature is the exception, requiring an offset in addition to multiplication.

Last updated: June 2026