Getting the right size of nappy is really important to keep your baby comfortable and to prevent leaks. Nappies sizes relate to the weight of your baby.
Here's a handy guide for Pura nappies:
Size 1: newborn 2 - 5 kg / 4 - 11 lbs
Size 2: mini 3 - 6 kg / 6 - 13 lbs
Size 3: midi 6-10 kg / 13 - 22 lbs
Size 4: maxi 7-18 kg / 15 - 40 lbs
Size 5: junior 11 - 25 kg / 24 - 55 lbs
Size 6: xl 15+ kg / 33+ lbs
When putting the nappy on your baby, make sure the material around their legs and bottom is sat properly, ensuring it isn't caught or folded inside by running your fingers along the leg cuffs. Check that it's fastened properly, not too tight but not too loose, by testing that you can fit two fingers inside the waistband.