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# Calculate your own body mass index

## Video transcript

so let's talk about body mass index BMI this is a term that's often discussed and so let's first figure out how it's calculated how do we figure this out so if you have a little stick person what you could do is have them step on a scale and you get their weight so the first thing you need is their weight and then you go on and you ask them if they would mind if you would take their measurement of height and so you get their h or height and a BMI is basically just taking those two numbers and using them in a little equation where you take the weight divided by the height squared very simple right so now let me calculate my BMI but before I do that I have to tell you one more thing which is that the weight this is in kilograms kg and the height is actually in meters squared so when I was actually figuring out my own height and weight I realized a problem and I'll show you what that was so my weight is 160 pounds and my height is six foot one inch which is the same as 73 inches so I would love to use this easy equation but I have pounds and inches I don't have kilograms and meters so what do I do well what I need to do first is is convert over right so I can say all right well one pound one pound equals and this is something you can just look up on the internet 0.45 for kilograms so far so good and now one inch which is pretty small is going to be a small number relative to a meter which is huge right and so it's it is it's 0.025 for meters so now I've got my conversions and actually what I can do is I can take these numbers and plug them in here to help me easily convert from kilos and meters over to pounds and inches make my equation much simpler for me to use so I could say okay well now how about weight in pounds and height in inches squared and I have to multiply right because I have to multiply by the conversion and so I'll multiply by 0.45 4 divided by 0.025 4 squared and to make it even easier I can actually take this whole thing plug it into my calculator and it gives me the number 703 so I could say okay so really what I have here is again weight in pounds divided by height in inches squared multiplied by 703 so going back now I can finally throw in my own numbers right I can say okay so my BMI is 160 divided by 70 three times write that out 70 3 squared times actually times 703 so me a rates that just to make it clear okay so this mass works out to 21 so my BMI is 21 wonderful the next question is well what does that mean you know if I have a BMI of 21 is that normal or is that good or how should I feel about that so if you put a scale out here starting with 0 - let's say 30 and I have 25 here and let's say this is about eighteen point five what physicians have done is basically divided up the BMI into categories and they said okay well if your BMI as it is somewhere between zero and 18.5 somewhere in this range I'm going to do it in yellow then you're underweight I'm just going to write under and if you're between 18 point 5 and 25 if you're in this range you're in a very healthy range and so I'll write a little smiley face for that and if you're above 25 let's say 25 to 30 then you're in the overweight range and finally if you're above 30 let's say you're out here then you're obese and so that's where the word obese really comes from it comes from a category of BMI and so going back to my BMI I'm right here 21 and I'm doing pretty well but the question might come up in my head you know what weight would I be if I was overweight and what weight would I be if I was obese you know how many pounds away am i from being in those categories so I can go back to my equation BMI equals W over H squared and I can just rearrange it I could say okay well how about W equals BMI times H squared over 703 right because that's the conversion so if I rewrite the equation like this then now I can solve for my weight I can say okay well let's say that I wanted to figure out what to do if I have a BMI of 25 and I know that my height probably won't change I'm not going to grow anymore and 703 is the number we always have to use when we're using the conversion from pounds to kilos and inches to meters so what does that equal well in this particular case using 25 I can see that for me to be overweight I would be around 190 pounds 190 pounds so that's actually really really good to know that's actually 30 pounds above what I am today so that gives me a sense for how far away I am from being overweight and I can even do this for a BMI of 30 I can say what about a BMI of 30 my current height again is 73 inches that's not going to change and I can do the math and find out that in this case my weight would be 227 pounds so if I was 227 pounds given my height I would be considered obese