Genetics also play a part in how much your child weighs. Look at your baby pictures. Were you all dimples and dumpling, or long and lean? Other factors, including nutrition and the health of the mum during pregnancy, can affect a child's size.
But as little ones grow, it's not how heavy they are at any given time that's important, it's the rate at which they gain weight. Every child follows a set pattern of growth from birth.
Straight after birthThe first thing babies do on their pattern of growth is shrink! It takes a while for your newborn to get used to drinking milk rather than getting food through the placenta (and if you're breastfeeding, for you to start making it), which means he can lose up to 10% of his weight in the days following birth.
But by about 10 days old, he should start to put it on again. Your health visitor will plot your baby's weight gain for the first few weeks (then less regularly as he grows up) in his health record on a growth chart, also known as a centile chart.
The lines represent a zone within which your baby is expected to grow normally. If he's on the top line, or centile, it doesn't mean he's overweight. Equally, he's not underweight if he's on the lower line. Either way, he's still within what's considered the normal range.