I have my computer set up for Km. I often have to converts to mile when talking to people. The easy conversion which is accurate enough for most purposes is 3/5, i.e. multiply the number of kilometers by three and then devide by five. You can easily do that in your head. There are approximately 5 kilometers in three miles. If you are using a calculator you may simply devide the kilometers by 1.61 to get a more accurate miles, or multiply miles by 1.61 to get kilometers.