Join Date: Jun 2004
Location: Northern Nevada
Sixteen and 27 inches would be extreme sizes--16 is tiny and 27 is huge. In that case, I think they're talking about the wheel diameter, which is common in cheap US-market bikes but doesn't really tell you much.
The way bikes are REALLY measured is by frame size, from the center of the bottom bracket (the spindle at the bottom that holds the crankarms) up along the seat tube to either the top of that tube or the center of the top tube, which is the one that runs forward from the seat toward the handlebars.
Most manufacturers now go center to top, I think. In the old days, road bikes were usually center-to-center, but mountain bikes were center-to-top. Road bike measurements typically are given in centimeters (2.54 per inch). Mountain bikes are often expressed in inches, but you'll see them in centimeters sometimes, too.
"Twenty-seven inch" used to be the standard for American road bikes, and referred to the wheel diameter. Those now use "700C" wheels, which are metric and close to the same size, but not interchangeable.