📏 Unit Converter
Convert length, weight, temperature, volume, speed and data units. Free, unlimited, private — works entirely in your browser.
How to use
- Pick a category: length, weight, temperature, volume, speed, area, time, or data.
- Enter the value you want to convert in the input field.
- Choose the from unit and the to unit from the dropdowns (for example miles to kilometers).
- The result converts instantly as you type — tap the swap button to reverse the direction.
FAQ
Is it really free?
Yes — every tool on this site is 100% free with no limits, no signup and no watermarks.
Is my data private?
Absolutely. All processing happens locally in your browser. Your files are never uploaded to any server.
Which unit categories are supported?
Length, weight/mass, temperature, volume, speed, area, time, and digital data — covering metric (SI), imperial, and US customary units, plus specialty units like knots, acres, and bytes.
How accurate are the conversions?
Conversions use exact defined factors (1 inch is defined as exactly 2.54 cm), so results are as precise as your input value. Temperature uses the standard offset formulas between Celsius, Fahrenheit, and Kelvin.
Can it convert between metric and imperial systems?
That is its main job — kilograms to pounds, liters to gallons, Celsius to Fahrenheit, miles to kilometers — in either direction, instantly.
Why does temperature need a formula instead of a simple factor?
Because temperature scales start at different zero points. Converting degrees C to degrees F is not a multiplication but (C × 9/5) + 32. The tool applies the correct formula automatically, including the Kelvin offset of 273.15.
Complete Guide to Unit Conversion
Two measurement systems run the world: the metric system (meters, kilograms, liters), used by nearly every country and all of science, and the imperial/US customary system (feet, pounds, gallons), still standard in the United States and parts of the UK. Converting between them is a daily need for travelers, cooks, students, and engineers — and anyone reading an American recipe or a European car spec sheet.
Conversions you will actually use
- Travel: miles to kilometers (1 mile = 1.609 km), Fahrenheit to Celsius for weather, gallons to liters for fuel economy.
- Cooking: cups to milliliters, ounces to grams, Fahrenheit to Celsius for oven temperatures (350°F = 177°C).
- Health and fitness: pounds to kilograms, feet/inches to centimeters, miles to kilometers for running.
- Tech: inches to centimeters for screen sizes, Mbps for internet speed, GB/MB for storage.
Why precision matters
In 1999, NASA lost the $125 million Mars Climate Orbiter because one team used metric newton-seconds while another used imperial pound-seconds — a unit mismatch that went unnoticed until the spacecraft burned up in the Martian atmosphere. The lesson: always label your units, and convert explicitly rather than guessing.
Quick mental tricks: Celsius to Fahrenheit is roughly double and add 30 (close enough for weather). Kilometers to miles is roughly multiply by 0.6. Kilograms to pounds is roughly double and add 10%. For anything where accuracy counts — medicine, engineering, baking — use the converter instead of approximations.
How the two systems evolved
The metric system was born in revolutionary France (1790s) from a simple idea: base everything on powers of ten. A meter was defined from the Earth itself, a kilogram from water, and every larger or smaller unit is just a prefix - milli, centi, kilo. The imperial system grew organically over centuries: a foot was literally a foot, an acre was what oxen could plow in a day. The US customary system descends from British units but diverged - a US gallon (3.785 L) is smaller than an imperial gallon (4.546 L), a classic trap for travelers.
Everyday conversion reference
- Length: 1 inch = 2.54 cm; 1 foot = 30.48 cm; 1 yard = 0.914 m; 1 mile = 1.609 km
- Weight: 1 ounce = 28.35 g; 1 pound = 453.6 g; 1 stone = 6.35 kg
- Volume: 1 fl oz = 29.57 ml; 1 cup = 236.6 ml; 1 pint = 473 ml
- Temperature: 0C = 32F (freezing); 20C = 68F (room); 37C = 98.6F (body); 100C = 212F (boiling)