Since road bikes are often used for commuting and longer rides, it's imperative that you attain the right fit when you purchase your bike. Not only will your torso and arm length help you decide the size of bike you select, but the measurements can help you correctly adjust your bike for the most comfortable ride. Using a measuring tape to determine the length of your torso and the length of your shoulder to your hand will ensure that you're able to get the best fit possible.
Ask a friend to help you take your measurements. Stand against a wall, with your feet 6 to 8 inches apart.
Stretch your arm out to the side. Have your friend measure from your collarbone to the center of your hand. This is your shoulder measurement, and you'll use it to adjust the handlebars.
Place a book -- spine up -- snugly between your legs and resting firmly against your crotch. Have your friend stretch the measuring tape from just above your sternum down to the top of the spine of the book to find your torso measurement. This will allow you to purchase the right bike and adjust your seat the proper length from the handlebars.
Give your measurements to a retail associate at a cycling store. Armed with your torso and arm measurements, along with an inseam measurement from your crotch to your heel, you'll be able to select a bike that closely suits your measurements and that can be further adjusted to suit your specific size. Your arm and torso measurements will be used to adjust the seat and handlebars.