Finding the X-seam

You'll need a measuring tape and a board that is approximately 30" to 48" long (an ironing board will work). Place one end of the board on the floor, then put the entire board flush against any wall, then pull the bottom of the board about 14" to 16" away from the wall. This should simulate a comfortable reclined position, like you'd have in a car. Now remove your shoes, sit on the floor, and pull your butt tightly against the bottom of the board (by holding the board steady in its position with your hands while gently scooting your butt against the board). Then stiffen your legs straight out (no bending of the knees), and point your toes straight up towards the ceiling. Now take the measurement from the base of the reclined board to the bottom of your shoeless heel. VOILA! You now have your x-seam measurement, which will determine what size bike frame you'll need to order.

HINT #1 - You can place a book at the base of your heel before you've straightened out your legs, then once your legs are straight, you can get up and measure from the base of the board to the point at which your heel left the book.

HINT #2 - You may want to repeat the measuring process from start to finish, to ensure that your x-seam measurement is correct, if only for peace of mind.

Finding the K-seam

Ok, you've measured the x-seam. Now, before you get up, take another measurement from your heel to the narrowest part of your leg (just below the knee cap at the top of the calf muscle). This is the k-seam measurement, which helps us put the handlebars in the right place.

Your recommended frame size (based on the x-seam) is:

Frame Size X-seam
X-small 35" - 38"
Small 36.5" - 39.5"
Small / Med 38" - 41"
Medium 39" - 42"
Medium / Large 40" - 43.5"
Large 41.5" - 45"
X-large 44" - 48"