Free Online Unit Converter — Length, Weight, Temperature, Volume, Area & Speed
Paste a number, pick your units, and get the result instantly. Our free unit converter handles length, weight, temperature, volume, area, and speed — all in one place, with no sign-up and no limits on how many conversions you run.
Whether you're converting meters to feet for a construction project, Celsius to Fahrenheit for a recipe, or kilograms to pounds for a shipping label — this tool shows you the answer in real time alongside a full conversion table for every unit in the category.
How to Use the Unit Converter
- Select a category — click Length, Weight, Temperature, Volume, Area, or Speed at the top.
- Enter your value — type the number you want to convert in the FROM field.
- Choose your units — select the source unit (FROM) and target unit (TO) from the dropdowns.
- Read the result — the converted value appears instantly in the TO field.
- Copy or swap — use the copy button to grab the result, or hit the swap icon to reverse the conversion direction.
The reference table below the converter shows your input value converted to every unit in that category at once. Click any row to set it as your TO unit.
Metric vs Imperial — Why Conversion Matters
Most of the world uses the metric system (SI), where every unit is a power of ten apart — 1 km = 1,000 m, 1 kg = 1,000 g. The United States still uses customary units (feet, pounds, gallons, Fahrenheit), making cross-border communication a constant conversion problem.
Temperature is the trickiest because Celsius, Fahrenheit, and Kelvin all have different zero points. Converting 0°C to Fahrenheit gives 32°F, not 0°F — because the scales start at different reference temperatures. For length, weight, volume, area, and speed, conversion is straightforward multiplication by a fixed factor.
Common Use Cases
- Construction and DIY: Convert feet and inches to centimeters when working with European materials or floor plans. Blueprint dimensions often mix metric and imperial.
- Cooking and recipes: International recipes use metric measurements (mL, grams, liters). Convert cups, tablespoons, and ounces on the fly without mentally doing the math.
- Travel and shipping: Speed limits in km/h vs mph, luggage weight in kilograms vs pounds, distances in kilometers vs miles — all covered.
- Science and school: Convert between SI units for lab reports, physics homework, or exam prep. Our converter shows formulas in the FAQ to help you learn, not just copy answers.
- Engineering: Technical drawings, material specs, and flow rates often need conversion between metric and imperial. Length, area, volume, and speed — all in one place.
Frequently Asked Questions
How do I convert meters to feet?
Multiply meters by 3.28084. For example, 5 meters equals 5 × 3.28084 = 16.4042 feet. The exact conversion is 1 meter = 3.280839895 feet, defined because 1 foot = exactly 0.3048 meters since 1959. Our converter applies this instantly — just type the value and select m → ft.
How do I convert Celsius to Fahrenheit?
Use the formula °F = (°C × 9/5) + 32. For example, 100°C = (100 × 9/5) + 32 = 212°F (boiling point of water). For body temperature: 37°C = 98.6°F. To convert the other way, use °C = (°F − 32) × 5/9. Our converter handles both directions and also converts to Kelvin.
How many kilograms are in a pound?
1 pound equals exactly 0.45359237 kilograms, so 1 kilogram = approximately 2.20462 pounds. A quick mental shortcut: multiply pounds by 0.45 for a rough kilogram estimate. For cooking, 1 ounce ≈ 28.35 grams and 16 ounces = 1 pound = 453.59 grams.
How many liters are in a gallon?
1 US liquid gallon = 3.78541 liters. The UK imperial gallon is larger at 4.54609 liters — about 20% more. Always check which standard applies; recipes and fuel economy figures use different gallons depending on the country. 1 US cup = 236.588 mL, and 1 liter ≈ 4.23 US cups.
What is a knot in km/h and mph?
1 knot equals exactly 1.852 km/h, or approximately 1.151 mph. Knots are used in aviation and maritime navigation because 1 nautical mile corresponds to 1 arcminute of latitude on Earth — making them naturally suited to navigation. Wind speeds in international aviation forecasts are given in knots.
Resources
- NIST — Guide to the SI (International System of Units) — Official US government reference for SI unit definitions, prefixes, and exact conversion factors.
- Wikipedia — United States customary units — Complete reference for US customary unit definitions and their official metric equivalents.
