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Unit Converter

Convert length, weight, temperature, and speed units.

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Our free Unit Converter lets you quickly convert between common units of measurement. We currently support four essential categories: length, weight/mass, temperature, and speed. Each category includes both metric and imperial units, covering everyday conversion needs.

To use the converter, select the category first, then choose the unit you are converting from and the unit you are converting to. Enter your value in the input box, and the result appears instantly. All conversions use highly accurate conversion factors sourced from international standards.

Length conversions include millimeters, centimeters, meters, kilometers, inches, feet, yards, and miles. Weight covers milligrams, grams, kilograms, metric tons, ounces, pounds, and short tons. Temperature converts between Celsius, Fahrenheit, and Kelvin using the standard formulas. Speed supports m/s, km/h, mph, knots, and ft/s.

All calculations happen in your browser, so the tool works offline and your data is never sent anywhere. Results are shown with appropriate precision — generally 4 to 6 significant figures — to avoid misleading false precision while maintaining useful accuracy.

Frequently Asked Questions

What units are supported?
Length: mm, cm, m, km, in, ft, yd, mi. Weight: mg, g, kg, tonne, oz, lb, ton (US). Temperature: °C, °F, K. Speed: m/s, km/h, mph, knots, ft/s. Contact us if you would like additional units added.
How accurate are the conversions?
We use exact international standard conversion factors (e.g., 1 inch = 2.54 cm exactly, 1 pound = 0.45359237 kg exactly). Results are computed using double-precision floating point arithmetic and rounded to 6 significant figures.
Why does converting Fahrenheit to Kelvin take two steps?
Fahrenheit and Kelvin use different zero points as well as different-sized degrees, so the conversion requires both an offset and a scaling. Our tool computes the correct result directly: K = (°F + 459.67) × 5/9.
Is this tool accurate enough for scientific or engineering use?
For most everyday, educational, and general engineering uses, yes. For critical scientific or metrological applications requiring the highest precision, consult a NIST-traceable reference, as rounding and floating-point behavior may matter at extreme precision.

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