Children's bikes are generally measured by wheel size, rather than by frame size. Remember children do grow very quickly and you need to take this into consideration when buying a kids bike, However, if you buy a bike that is simply too big for your child, you will compromise your child's safety, and ultimately discourage your child from cycling.
Age of Child
Which Size Bike Do I Require?
Adults bikes and those for 10/11 years and over, are generally measured by frame size. This is normally the measurement between the centre of the bottom bracket to the top of the seat tube.
This CHAIN WEAR INDICATOR TOOL contains the following features as listed below:
TO USE THIS CHAIN WEAR TOOL SIMPLY PLACE ONE END INTO A LINK ON YOUR CHAIN AND IF THE 0.75% SIDE FITS IN YOU WILL NEED TO REPLACE YOUR CHAIN SOON. IF THE 1% FITS IN YOU NEED TO CHANGE YOUR CHAIN IMMEDIATELY