How Tall will my Children Be?

There are various formulas to work out how tall your baby will grow to as an adult, based on the height of the parents - do they work?  Logic would suggest that they can't do, because otherwise siblings would all be the same height!  But then, look carefully at how to apply the formulas...generally you take the height of the mother and father, add them together and divide by two (ie. take the average height of the parents).  Then they may make an allowance for boys (add a bit on) or girls (take a bit off) and that produces your answer.   BUT, they state that this gives you an estimate plus or minus 10 centimeters.  Plus or minus 10cm?!  That's hardly an accurate prediction!

Others state that you simply take the height of the child on their second birthday and double it, and that that will give you an accurate figure for how tall your babies will be when fully grown.  We can't find any scientific studies that confirm this, do you have your old height records that you can use to help us prove or disprove this theory?