Introduction
This Unit Converter Calculator changes one unit into another. Type a number, pick your two units, and see the answer right away. It works for length, weight, temperature, volume, area, speed, time, pressure, energy, power, angle, and frequency.
Need centimeters to inches? Kilograms to pounds? Celsius to Fahrenheit? Miles to kilometers? Liters to gallons? Just tap a category or use a quick link. You can also search for a unit by name, symbol, or nickname, like "lbs" or "kph".
The tool shows more than a number. It gives step-by-step math so you can see how the answer was found. It also lists your value in every unit of that group and draws a chart to compare them. You can set how many digits you want, swap the units with one click, and copy the result.
Use it for school work, cooking, travel, DIY projects, science class, or shipping. It is free, fast, and easy to use on a phone or computer.
How to use our Unit Converter Calculator
Pick a category, type a number, and choose your units. The tool shows the converted answer, the math steps, a table of every unit, and a bar chart.
Measurement Category: Click a tab like Length, Weight, Temperature, or Speed. This sets the list of units you can pick from.
Value to convert: Type the number you want to change. You can use decimals, negative numbers, and science notation like 1.5e3.
From unit: Choose the unit your number is in now, such as meters, pounds, or Celsius.
To unit: Choose the unit you want the answer in, such as feet, kilograms, or Fahrenheit.
Converted result: Read your answer here. You can also type in this box, and the "From" value will convert backward.
Swap button: Click the arrows to flip the two units and convert the other way.
Result Precision: Pick how many digits you want in the answer. More digits give a more exact result.
Find Units to Convert: Type a unit name, symbol, or nickname, like "kg" or "lbs". Pick one from the list and click Find Conversion. Only one box is needed.
Common Conversions: Click a quick link like "kg → lbs" or "Celsius → Fahrenheit" to set up that conversion in one step.
Buttons: Use Calculate to update the result, the X to clear both values, the copy icon to copy your answer, and Reset to start over.
What Is Unit Conversion?
Unit conversion means changing a measurement from one unit to another without changing the actual amount. A person who is 6 feet tall is also 1.83 meters tall. Both numbers say the same thing. Only the unit changed.
Every conversion works with a conversion factor. That is a number that links two units. For example, 1 inch equals 2.54 centimeters. So you multiply inches by 2.54 to get centimeters, or divide centimeters by 2.54 to get inches.
Measurement Systems
Most conversions move between two main systems:
- Metric (SI): meters, grams, liters. Units grow and shrink by powers of 10, so math is easy. Used by most of the world.
- Imperial / US customary: inches, feet, miles, pounds, gallons. Used mostly in the United States. The steps between units are not round numbers (12 inches in a foot, 5,280 feet in a mile).
Watch out for units that share a name but not a size. A US gallon (3.785 liters) is smaller than an imperial gallon (4.546 liters). A US ton (2,000 pounds) is lighter than an imperial long ton (2,240 pounds).
Common Conversion Factors
- 1 inch = 2.54 centimeters
- 1 foot = 0.3048 meters
- 1 mile = 1.609 kilometers
- 1 kilogram = 2.205 pounds
- 1 liter = 0.264 US gallons
- 1 acre = 4,047 square meters
- 1 kilowatt = 1.341 horsepower
Why Temperature Is Different
Most units only need multiplying. Temperature also needs adding or subtracting, because the scales start at different points. Water freezes at 0 °C but at 32 °F. To go from Celsius to Fahrenheit you multiply by 9/5, then add 32. To go back, subtract 32, then multiply by 5/9. Kelvin starts at absolute zero, the coldest possible point, so Kelvin equals Celsius plus 273.15.
Squared and Cubed Units
Area and volume units follow the same rule, but the factor gets raised to a power. Since 1 foot is 0.3048 meters, 1 square foot is 0.3048 × 0.3048 = 0.0929 square meters. And 1 cubic foot is 0.3048 × 0.3048 × 0.3048 = 0.0283 cubic meters. This is why a small length change makes a big area or volume change.
Where Conversions Matter
Cooking uses cups, milliliters, and grams. Travel uses miles, kilometers, and Celsius, along with time zone math. Building and DIY work uses inches, millimeters, and square feet. School science uses meters, joules, and newtons. Shipping uses pounds and kilograms. Getting the unit wrong can cost money or ruin a project, so it helps to double check the factor before you build, bake, or buy.
Tips for Accurate Results
- You can only convert units that measure the same thing. Meters cannot become kilograms.
- Round only at the end. Rounding early builds up error.
- Keep more digits for science and engineering work, fewer for everyday use.
- Always write the unit next to the number so nobody has to guess.