I would use a sizing chart before ordering the bike. I would also find my correct inseam measurement. In order to determine the standover height, just measure from the ground, up to the horizontal top tube. Your inseam should be greater than your standover height, by about 1-2inches.

In order to find your inseam measurement, tie a sinker or heavy earring to four feet of fishing line or thread. Place the sinker end on the floor while you're stand up, holding the line. Now take a grade school math book, open it to the middle page and place the line near the back of the spine of the opened book. Now close the book, leaving only about five inches of line, hanging outside the book. Now slide the face of the book up your leg and stop just before you get to your genitalia.

At this point, you'll need another person to make certain that the book is perfectly perpendicular to the floor. Have this person pull down on the over hanging fishing line, until the sinker just barely touches the floor. Now with a pair of scissors, cut the line along the edge of the book from which the line is hanging.

Tape the end of the line and the end the sinker, to the kitchen counter top. Now measure the total length of the line plus the sinker. That's your inseam measurement.

Alternatively, you could just follow these instructions, instead:
www.ehow.com/how_4672747_choose-right-size-bike.html

Furthermore, to get an even better idea:
www.rei.com/expertadvice/learn/bike+fit.html

Try to give Nashbar.com a call concerning bike size and fit tomorrow, due to the fact that some lines of bikes have their sizings set up differently.

1-(877)-688-8600 ---> NB Customer Service

- Slim

PS.

If you must error, error on the small side, NOT the large side. Bikes too large get sold to the higest bidder. We can always make a few minor adjustments for bikes just a tad too small.