swaddle blanket are amazing. they range from 36 inches to 47 inches. I've used them for my daughter since she was a newborn. now she's 18 months and we have her 47×47 swaddle blankets and we use those as cover at night. they are HUGE. and come in handy. they can also be used as breast feeding covers as well as carseat covers.
Receiving blankets are the ones used to wrap your baby after they're born and after a bath; Swaddle blankets are used to wrap baby up for their comfort to kind of like remind the baby of the womb, give them a feeling of security and helps baby sleep better. Keeps baby from flailing too so it can be really beneficial when breastfeeding