Unit Converter

What is a unit converter?

A unit converter changes a measurement from one unit to another, such as kilograms to pounds, centimeters to inches or Celsius to Fahrenheit. You type a number, choose the two units, and the answer appears instantly. There is no formula to remember and no calculator to open.

People use it every day: following a recipe from another country, checking a package weight, buying furniture, planning a trip, reading a weather forecast or helping with homework. Our converter covers seven everyday groups: length, weight, temperature, area, volume, speed and time.

Common conversions people look for

These are some of the most useful values to know. The converter above gives you more digits whenever you need them.

• Kilograms to pounds: 1 kg = 2.2046 lb, and 1 lb = 0.4536 kg.
• Centimeters to inches: 1 inch = 2.54 cm exactly.
• Feet to meters: 1 foot = 0.3048 m exactly.
• Miles to kilometers: 1 mile = 1.6093 km, and 1 km = 0.6214 miles.
• Liters to gallons: 1 US gallon = 3.7854 liters.
• Kilometers per hour to miles per hour: 1 km/h = 0.6214 mph.
• Celsius to Fahrenheit: Multiply by 9/5 and add 32.

Length: metric and imperial

The metric system builds on the meter, with kilometers, centimeters and millimeters as the common steps. The imperial and US customary systems use inches, feet, yards and miles. One inch is exactly 2.54 centimeters, one foot is 12 inches or 0.3048 meters, one yard is 3 feet or 0.9144 meters, and one mile is 1,760 yards or 1.609344 kilometers.

Here is a quick example. A person who is 5 feet 10 inches tall is 70 inches tall, and 70 x 2.54 gives 177.8 centimeters.

Weight and mass

In daily life we say weight when we mean mass, and converters follow the same habit. The kilogram is the base unit in the metric system, and one kilogram is 1,000 grams. A pound is 453.59237 grams, an ounce is about 28.35 grams, and a stone is 14 pounds or about 6.35 kilograms.

To convert pounds to kilograms, multiply by 0.45359237. For example, 150 lb is about 68.04 kg. To go the other way, multiply kilograms by 2.20462.

Temperature: Celsius, Fahrenheit and Kelvin

Temperature does not convert with a simple multiplication, because the scales start at different points. To change Celsius to Fahrenheit, multiply by 9/5 and add 32. To change Fahrenheit to Celsius, subtract 32 and multiply by 5/9. Kelvin is Celsius plus 273.15.

Some useful reference points: water freezes at 0 degrees Celsius (32 degrees Fahrenheit) and boils at 100 degrees Celsius (212 degrees Fahrenheit) at sea level. Normal body temperature is about 37 degrees Celsius, or 98.6 degrees Fahrenheit. The two scales meet at minus 40, where both show the same number. Absolute zero is minus 273.15 degrees Celsius, and nothing can be colder.

Area, volume, speed and time

• Area: 1 hectare = 10,000 square meters, and 1 acre is about 4,046.86 square meters.
• Volume: 1 US gallon = 3.785 liters, 1 US cup is about 237 milliliters, and an imperial gallon is 4.546 liters.
• Speed: 1 m/s = 3.6 km/h, and 1 knot = 1.852 km/h.
• Time: 1 hour = 60 minutes = 3,600 seconds, and 1 week = 7 days = 168 hours.

Metric vs imperial: which countries use what?

Most countries in the world use the metric system, officially called the International System of Units (SI). The United States still uses US customary units for most everyday things, and the United Kingdom mixes both: road signs show miles, while food is sold in kilograms.

Be careful with names that look the same. A US gallon and an imperial gallon are different sizes, and so are US and imperial pints. Our converter labels them clearly.

Tips for accurate conversions

• Use exact factors: Many conversions, such as 2.54 cm per inch, are exact. Do not round them in the middle of a calculation.
• Round at the end: Round only the final answer, to the precision you need.
• Check the unit type: US and imperial units share names but not values.
• Weigh ingredients when you can: For cooking, grams are more reliable than cups because the same cup can hold different amounts of flour.
• Double-check important numbers: For medicine, building work or travel documents, verify the result with a second source.

Common conversion mistakes

• Dividing instead of multiplying: Check whether the number should get bigger or smaller. Kilograms to pounds increases the number.
• Treating temperature like length: You must add or subtract an offset, not only multiply.
• Mixing US and imperial units: A US gallon is smaller than an imperial gallon.
• Confusing area with length: A square meter is not the same as a meter. Area conversion factors are squared.
• Rounding too early: Small rounding errors grow when you chain several conversions.

Why use our free unit converter?

• Seven groups in one tool: Length, weight, temperature, area, volume, speed and time.
• All units at once: See the value in every unit of the group with a single entry.
• Swap in one click: Reverse the direction without typing again.
• Private: Your numbers stay in your browser and are never uploaded.
• Free: No signup, no limits and nothing to install.