Miles (mi) are Imperial or English units used to measure distance, and kilometers (km) are metric units used to measure distance. Some devices, such as many car speedometers, measure and display both, but when the conversion is not already done, knowing how to change kilometers to miles can be a helpful skill. If you know the rate, you can quickly estimate the conversion.
- Understand the conversion rate
For every 1 mile, there are approximately 1.609 kilometers. Alternatively, you could think that each kilometer is 0.621 miles, (because 1/1.609 = 0.621).
- Multiply by the rate
When converting units, use fractions to cancel out the unit you no longer want by putting it on the opposite side of the fraction. To turn kilometers into miles, multiply a given number of kilometers by either the fraction 0.621mi/km or the fraction 1mi/1.609km. For example, 100km * 0.621mi/km = 62.1mi, because the kilometers cancel. 85km * 0.621mi/km = 52.8mi
- Check your answer
Whether you estimated or used a calculator, check your answer to make sure it makes sense. Because the conversion rate is 0.621, you know that the answer should be between 0.6 (or 3/5) and 0.667 (or 2/3). In the second example, 0.6 * 85 = 51, and 0.667 * 85 = 56.67. The calculated answer, 52.8, is between 51 and 56.67.