According to the regulation, child restraint systems are classified into different groups according to the mass of the child. The groups defined by the ECE R 44/04 standard are:
GROUP 0 From Birth to 10 Kg
GROUP 0+ From Birth to 13 kg
GROUP I From 9 to 18 kg
GROUP II From 15 to 25 kg
GROUP III From 22 to 35 kg
The various child restraint system models can be in a single group or a combination of them.