How to measure frame size kids bike The way I know how to measure frame size is by measuring from the center of the cranks to to top of the seat tube.

I ordered a 16" bike from Halfords but the seat tube is only 9". On the box it says 16" x 9" what???? sso where does the 16" come from?

So my neice is 115cm tall. According to halfords size guide a 16" will be fine for her since her daddy has got her a 14" but thats in london.

Is it me thats order the wrong size or has the oem packed in the wrong bike?
Youth bike sizing is traditionally done by the wheel size. Check your tires they may say 16". 

Other possibility is the 16" is top tube length (from center of seat post to center of headset traditional measurement)