Select a category at the top, such as Length, Weight, or Temperature. Then type your value in the left box and pick the unit you are converting from. Choose the unit you want on the right. The converted value appears instantly. Hit the swap button in the middle to reverse the conversion direction.
Most countries use the metric system, also called SI (International System of Units). It is built on powers of 10, which makes it easy to work with. 1 kilometer is exactly 1,000 meters. 1 kilogram is exactly 1,000 grams. The pattern is consistent.
The United States uses the US customary system. Its relationships are less tidy. There are 5,280 feet in a mile and 16 ounces in a pound. Scientists everywhere prefer metric because consistency matters in research. But knowing both systems is genuinely useful in everyday life.
| From | To | Multiply By |
|---|---|---|
| 1 inch | centimeters | 2.54 |
| 1 foot | centimeters | 30.48 |
| 1 mile | kilometers | 1.609 |
| 1 kilogram | pounds | 2.205 |
| 1 ounce | grams | 28.35 |
| 1 US gallon | liters | 3.785 |
| 0°C | Fahrenheit | = 32°F (freezing) |
Every conversion comes down to one idea: multiply by a conversion factor. A conversion factor is a ratio that equals exactly 1. For example, 2.54 cm / 1 inch is a conversion factor because 1 inch and 2.54 cm are the same length.
To convert 5 inches to centimeters, you multiply 5 inches by (2.54 cm / 1 inch). The inch units cancel out and you are left with 12.7 cm. This approach, called dimensional analysis, works for every unit in every category.
