To not understand my child's bmi and weight centile

[PinotAndPlaydough]

My daughter is 4 and is currently being seen by the paediatric department she's had a consultation and I've recieved a letter from them, part of which has documented her height, weight and bmi.
The letter says that her weight is 30.6 and on the 49th centile yet her bmi is 16.5 and on the 52nd centile. Her height is 136.4 and on the 44th centile (so presumably just below average).

I'm so confused is her weight slightly below or is above average as her bmi is over the 50th centile (I've written centile that may times now it sounds like a nonsense word).

SummerNights

BMI is easy to calculate. In SI units, it's weight (kg) divided by height squared (metres). Therefore for fixed weight, the larger your height, the smaller BMI you have. Thus, if two people lie on the same percentile for weight, the one with a lower percentile for BMI would be the taller one.

If we assume that BMI somehow measures good proportion (not saying that it does, but let's assume) then people in the middle BMI range (say 30 - 70 percentile) will be some kind of "normal" shape. what your DS's figures suggest is that while he is very heavy (less than a percent of children his age are heavier), he is also very tall (only two percent taller), and thus is reasonably well proportioned with a middle of the range BMI.

It's not your daughter's letter, so phone them today

The weight is around 4.5 stone and the height is about 4ft 6.

Not everyone can be smack on the 50th centile, that's not how averages work!

Summer, I suspect that your son's measurements are not as you expect because at the extreme top of the centiles there are more very heavy children than there are very tall children, and that's why your very tall, proportionately broad child is "only" 98th centile. He's been pushed a bit down the weight curve because there are some seriously obese children up there who shouldn't be IYSWIM. (Redstrawberry seems to have accidentally read your figures the wrong way around)

But you don't need to worry about your child as long as he stays around that 60% mark and doesn't creep up towards the 80s.

135cm is the height they need to be not to use a booster seat any more, I think. So upper juniors age for most kids.

Redstrawberry seems to have accidentally read your figures the wrong way around

indeed. I did.

it doesn't matter. I thought the question was how could someone be in both the high 90s for weight and height and only 60 in BMI? it's because BMI is inversely related to height (height up, bmi down).

the other thing to note is that it is not a race. you aren't trying to get high numbers.