Your inseam is the distance from your groin to the floor. To measure, stand barefoot with a 6 inch gap between your feet. Place the spine of a book between your legs as high up as it will go, so it feels like you are sitting on a saddle, and have someone measure from the top of the book to the floor.
If you want to find the size of your current bike, measure from the center of the crank to the top of the seat post tube.
Remember, sizing charts are approximate. If you have extra long legs, an extra long torso, or just like the feel of a bigger or smaller bike, you may want to size up or down. Additional adjustments can be made by moving the saddle forward or back, and by adjusting the height and/or angle of the handlebars. We recommend sitting on a similar size frame locally before placing an order so that you get the size that's best for you.