Cyclocross - What FD clamp size do I need on my cross bike?

I'm trying to figure out what size FD clamp I need for my Raleigh Team Cross. I have no idea what year it is as it isn't shown in the Raleigh catalogs (The 2005 catalog shows the Team Cross but in different colors/decals).

Any ideas? Or advice on how to measure...

Here is the bike for reference (again). I've since added a road triple and new Tiagra 9x3 shifters and new bar tape.

http://i733.photobucket.com/albums/ww335/telepciaka/Raleigh%20Team%20Cross/100_0517.jpg

Measure the diameter of the seat tube at the place where the front derailleur will attach.

If you have a measuring caliper, use that to measure the diameter directly. Sizing is metric, so if your caliper is English-only, just remember there are 25.4 mm in an inch (exact conversion).

If you have a flexible measuring tape, you can measure the circumference and divide by pi (3.14159 blah blah blah) to get the diameter.

If you don't have a flexible measuring tape, you can take a string, wrap it around, then hold it up against a ruler or rigid measuring tape.

Your calculated measurement will probably be a little off, of course, but there are only so many sizes they make - just round it. :)

Thanks guys. I don't have a caliper, but with a string and measuring tape I got a circumference of 101mm / pi = 32.15. Close enough to 31.8 I assume?

Thanks again. I'm almost ready to climb some hills with this thing! I'll post pics when it is "complete".