First you’ll need to determine your pubic bone height (PBH). You’ll need a wooden dowel* (something like a broom handle will do), a metric tape measure, and a helper. In bare feet, stand with your feet flat on the floor, 10″ apart. Place the dowel between your legs, and while pulling it upward with a force that approximates sitting on a saddle, have your helper measure the distance from the floor to the top of the dowel in centimeters. This measurement is your pubic bone height. To be sure you get an accurate reading, repeat the process a few times while making sure to keep the dowel level. Once you’re sure you have a good number, write it down or send it to yourself in an email so you have it for your next bike purchase.
Once you have your PBH, it’s simple to calculate your saddle height. Here’s the Rivendell math:
PBH – 10 to 10.5cm = SH
And the LeMond math:
PBH x .883 = SH
Once you have your SH number, adjust your saddle to the proper height by measuring along the seat tube from the center of the bottom bracket (where the cranks bolt on) to the top of the saddle. Note that Rivendell recommends adjusting the math slightly for extreme crank lengths, but for the large majority of people riding either 170mm or 175mm cranks, these numbers are good.