Why does BMI have units of kg/m^2 when we are three dimensional? Wouldn’t kg/m^3 or g/cm^3 be more accurate?
In: 100
How does one compare how overweight/underweight one person is to another?
It’s not the absolute weight. You have to take height into account.
Turns out height squared works consistently to compare people’s weights over a wide variety of heights and weights.
People’s (volume) cm^3 doesn’t track with their weight as much as the square relationship of height
If it were kg/m^3 then it would just be proportional to density. The idea of BMI is that there is a healthy range of weights for people. Fatty tissue has a slightly different density than lean muscle, but not that different, so BMI wouldn’t be very sensitive if it were just the density.
So, knock off a length factor and you have something that correlates well with fitness. You can think of it like, you get one factor for height, but your girth, you only get one factor even though it’s 2d.
BMI is a ratio of body weight in relation to height, so if you changed the ratio it wouldn’t matter. A healthy person with a bmi of 20 wouldn’t be classified as obese because the scalings also change along with the formula. Different number, same bmi, just like how converting dollars into different currencies doesn’t make you more wealthy.
BMI is a ratio of body weight in relation to height, so if you changed the ratio it wouldn’t matter. A healthy person with a bmi of 20 wouldn’t be classified as obese because the scalings also change along with the formula. Different number, same bmi, just like how converting dollars into different currencies doesn’t make you more wealthy.
BMI is a ratio of body weight in relation to height, so if you changed the ratio it wouldn’t matter. A healthy person with a bmi of 20 wouldn’t be classified as obese because the scalings also change along with the formula. Different number, same bmi, just like how converting dollars into different currencies doesn’t make you more wealthy.
If you were using weight:volume you would end up with a number close to one. Water is 1g/cm^3. Being a very large proportion water we would be around there.
It would also be counterintuitive since fat is less dense than water. Using volume a more overweight person would have a LOWER BMI than a person with a healthy weight. Since this doesn’t align with more weight being a higher number it would confuse people
If you were using weight:volume you would end up with a number close to one. Water is 1g/cm^3. Being a very large proportion water we would be around there.
It would also be counterintuitive since fat is less dense than water. Using volume a more overweight person would have a LOWER BMI than a person with a healthy weight. Since this doesn’t align with more weight being a higher number it would confuse people
If you were using weight:volume you would end up with a number close to one. Water is 1g/cm^3. Being a very large proportion water we would be around there.
It would also be counterintuitive since fat is less dense than water. Using volume a more overweight person would have a LOWER BMI than a person with a healthy weight. Since this doesn’t align with more weight being a higher number it would confuse people
It has units of kg/m^2 because it is weight over height squared, basically.
On a population level it works: BMI has a correlation with various things, and because it works off data you *have*, it is better than no measure.
On an individual level it is not a good measure of obesity: it just isn’t a very good measure of body fat percentage for people who are not of average height. Better individual measures exist but they use data most people haven’t provided, like the circumference of the neck or a caliper measurement.
In other words, your surmise that something without the right units is not a good measure is a decent engineering intuition.
It has units of kg/m^2 because it is weight over height squared, basically.
On a population level it works: BMI has a correlation with various things, and because it works off data you *have*, it is better than no measure.
On an individual level it is not a good measure of obesity: it just isn’t a very good measure of body fat percentage for people who are not of average height. Better individual measures exist but they use data most people haven’t provided, like the circumference of the neck or a caliper measurement.
In other words, your surmise that something without the right units is not a good measure is a decent engineering intuition.
Latest Answers