Mountain bike tyre sizes are usually stated in inches.
Road bike tube sizes.
Kids bikes will have smaller wheels usually 16in 20in or 24in and need smaller diameter inner tubes and tyres as will most folding bikes.
The recommended wheel and tyre sizes should be.
Once you know your tire size see the method at the bottom of this page scroll down the list until you get to your tire diameter e g.
Below is the list of my recommended inner tubes.
Bike inner tube size chart and my recommendations.