Free online unit converter for length, weight, temperature, volume, area, and speed. Convert metric and imperial units instantly with real-time results.
A unit converter is a tool that converts a value from one unit of measurement to another within the same category, such as length, weight, temperature, volume, area, or speed. It supports both metric and imperial systems, giving instant, accurate results without manual conversion formulas.
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Overview
A unit converter is a tool that translates a measurement from one unit into another within the same physical quantity — turning kilometers into miles, kilograms into pounds, or Celsius into Fahrenheit. It removes the mental math and the risk of error when you work across measurement systems.
The world runs on two main systems: the metric system (meters, kilograms, liters, Celsius), used by most countries, and the imperial / US customary system (feet, pounds, gallons, Fahrenheit), used primarily in the United States. A good converter bridges both instantly.
How it works
Behind the scenes, every conversion uses a shared base unit per category. For length, that base is the meter: each unit stores how many meters it represents (1 foot = 0.3048 m). To convert, the value is first turned into the base unit, then divided by the target unit's factor.
Temperature is the exception — it is an affine conversion with an offset, not a simple ratio. Converting Celsius to Fahrenheit multiplies by 9/5 and adds 32, which is why 0°C equals 32°F, not 0°F.
Everyday use
Cooking from a foreign recipe (cups to milliliters), traveling abroad (miles to kilometers, Fahrenheit to Celsius), shopping for international products (pounds to kilograms), DIY and construction (square feet to square meters), or checking driving speeds (mph to km/h) — unit conversion shows up constantly in daily life.
Using exact factors matters. Small rounding errors in recipes, medication doses, or engineering can compound into real problems, which is why this converter computes at full precision and only rounds the final display.
Tips
Always confirm which variant of a unit you mean — a US gallon and a UK gallon differ by about 20%, and a US fluid ounce differs slightly from a UK one. For weight, note that a "ton" can mean a metric ton (1000 kg), a US short ton, or a UK long ton.
For scientific work, prefer base SI units (meters, kilograms, Kelvin) as your reference point, then convert outward. This keeps a single source of truth and minimizes compounding rounding.
Quick tips
Metric ↔ Imperial
1 inch = 2.54 cm, 1 mile ≈ 1.609 km, 1 kg ≈ 2.205 lb, 1 liter ≈ 0.264 US gallons.
Temperature
°F = °C × 9/5 + 32. Water freezes at 0°C / 32°F and boils at 100°C / 212°F.
Use the swap arrow
Tap the swap button to instantly reverse the conversion without re-selecting units.
Export to PDF
Save or share any conversion as a PDF with one click — no sign-up required.
Enter a value, pick a category, then choose the units to convert from and to. The result updates instantly — no button to press. Use the swap arrow to reverse the conversion.
Length, weight, temperature, volume, area, and speed. Each category includes both metric (meters, kilograms, Celsius) and imperial/US units (feet, pounds, Fahrenheit, gallons).
Conversions use exact internationally-defined factors (for example 1 inch = 2.54 cm exactly). Results are rounded for readability but computed at full precision.
A US gallon is about 3.785 liters, while a UK (imperial) gallon is about 4.546 liters — roughly 20% larger. The converter lists both separately so you pick the right one.
Yes. Every conversion is completely free, works in your browser, requires no sign-up, and you can export the result to PDF with one click.