You can measure your swing speed using a golf monitor or via a sensor, like the Swing Speed Radar. You can also do it manually.
When we say manually: you have to hit at least ten golf balls in an actual golf course. Here are the things to do to determine your swing speed:
Drive ten golf balls in a driving range with a friend. Determine the yards each ball has traveled before it hit the ground. You can rely on your friend to make the estimate. Do not consider the rolling distance the balls make.
Also, disregard the longest and shortest drives, as they may be affected by other factors such as the wind. To get your average drive yardage, add the remaining distances in yards and divide by eight. Next, divide the average drive yardage by 2.3 to get your swing speed.
To illustrate, if you have average drive yardage of 190, divide it by 2.3, you will get 82.60mph as your swing speed.