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Zinn Online Frame-Size Calculator

Arguably the most important determiner of comfort on your bike is frame fit. With this simple program, you can use measurements you take of your body to instantaneously come up with a close approximation of the ideal frame geometry for you.

As I am unable to personally verify the measurements nor have I interviewed you to find out other details about your physiology and riding preferences that might affect frame size, this only can provide a close approximation of the ideal frame dimensions. I have also not included my normal thigh and lower-leg measurements to determine seat tube angle, since this is a bit more subjective. This abbreviated system also does not take into account special top-tube lowering and angling steps I take to accommodate tall riders - those I have to do on an individual basis. Same goes with crankarm length; the bottom bracket height this comes out with is based on a crank length that is a normal average to use for your height, but a custom extra-long crank would require a different bottom bracket height for pedal clearance. Nonetheless, the results of this calculator system provide a good place to start from and will likely be more accurate and useful than the personal frame fitting you might receive at numerous bike shops.

The measurements this program provides are as follows. The Seat Tube Length (a.k.a. "frame size") is measured "center to top," i.e., from the center of the bottom bracket to the intersection of the top of the top tube with the center of the seat tube. The Top Tube Length is horizontal measurement, whether or not the actual top tube is sloped. It is taken from the center of the seat tube (or seat post) horizontally to the center of the head tube. Note that this horizontal measurement is longer than the measurement that would be found by measuring the center-to-center length along a sloping top tube of a frame with the same virtual horizontal top tube length. This is especially critical to understand on a mountain bike, since virtually all models now have sloping top tubes.

Be careful to take the measurements correctly, having another person assist you. The measurements should be taken in bare or stocking feet. Thanks for trying this out, and have fun figuring out what your ideal bike (or close to it) might look like.

Let's Fit!

Lennard Zinn
President, Zinn Cycles, Inc.
Author of the best-selling books:
  -"Zinn and the Art of Mountain Bike Maintenance"
  -"Zinn and the Art of Road Bike Maintenance"
Also senior technical writer for VeloNews and velonews.com