Fitting a person to a bicycle can be a complex task. However, the very first thing to know is your Pubic Bone Height or PBH. We're a big fan of Rivendell's measuring method, which you can see here:
Subtract 11 from that and you'll know more or less your seat height, as measured from the center of the bottom bracket to the top of the saddle, though you'll need to ride and fiddle to make sure.
Our bicycles are often measured between the bottom bracket and the intersection between the top tube and seattube, or sometimes from the bottom bracket to the top of the seattube.
Feel free to write to us with your PBH and any fitting questions you may have for Bassi bikes here.