Road Cycling - Frame measurements

Hello,

I have acquired a Lemond Buenos Aires from my Grandfather who can't ride anymore. It's a really nice bike but I just bought a bike a couple of months ago and have no place for two bikes.

I'm planning on selling the bike on Ebay. The question I have is on measuring the frame. I see bikes listed as 52 cm, 54 cm, etc... Is this a measurement of the top tube or the tube that goes from the crank to the seatpost? And exactly where do you begin and end the measurement? Obviously it needs to be accurate since a centimeter or two can make a difference.

I've also looked on the bike and don't see a tag listing the frame size. Sorry if this is a really basic question! Thanks!

It is the length of the seat-tube, from the centre of the bottom bracket, up to the intersection of the top tube.
The upper intersection may be with the centre-line or the top edge of the top tube, and should be stated. (centre-to-centre, or centre to top)
If the top tube is sloping, then use a virtual horizontal top tube, based on the level of the front of that tube.

A measure for the horizontal length of the top tube (centre to centre at the intersections) is also useful.

If you're unsure of how to accurately measure, simply hold a yardstick with large clear metric markings from the crankbolt up the length of the seattube and take a sharp clear picture to post on ebay. Do the same with the top tube, from the center line of the headtube to the seat tube-top tube intersection.

Cool. Thanks guys!