There are 2,000 to 2,500 steps in a mile, depending on your stride length. Generally speaking, you'll have a longer stride if you're taller and/or walking faster, which means you'll take fewer steps in order to walk a mile.
It is also suggested that a person should walk 10,000 steps a day to help maintain good health. This will be between 4 to 5 miles, again depending on your stride length.
You can use a pedometer to measure the number of steps you're taking. If you don't want to purchase a dedicated pedometer, there are also many apps available for your phone that can provide the same function. Alternatively, you can also use a distance mapper like geodistance.com to trace your path and determine how long it is, then convert it from miles to steps.