New to cycling

[geckoGT]

Yes your sizing on a road bike is likely to vary, how tall are you?

Seat tube length seems to be less important with the popularity of compact geometry frames, it is the top tube that is more important now. You will see terms such as centre to centre, centre to top and relative seat tube used in bike sizing now which can make it confusing for the novice.

The best way to really know what you need is to get sized up by someone that knows what they are doing.