BMI to body fat %

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Replies

  • sijomial
    sijomial Posts: 19,809 Member
    Doesn't seem to work too well for me - older but fit with more muscle than most old farts my age (55).

    Gives me 26%
    My "guesstimate" is around 15% but haven't tested my BF for a quite a while.
  • WBB55
    WBB55 Posts: 4,131 Member
    Your formula 35.25%
    Cheap scale 31.8%
    Average of tapings 29.5%
  • zyxst
    zyxst Posts: 9,149 Member
    Formula - 39.316 BF%
    Dexa scan done in Feb 2015 - 50.9 BF%

    Though I've lost 10# since the scan, pretty confident I didn't lose 11% in body fat.
  • MissAbbee
    MissAbbee Posts: 41 Member
    The calculator gave me 31.19%, Body fat measured last night at one of those stand on scales at the gym came to 31.1%.. I'll take that.
  • WBB55
    WBB55 Posts: 4,131 Member
    edited August 2015
    I'm thinking this formula is assuming that, something like, a female at a BMI of 18=18%BF and a female at a BMI of 30=40%BF and it's just applying a conversion formula to reach those assumed BF% at those BMIs. **numbers are pulled out of my head** and then adding a little cojigger to assume older people have a higher BF%
  • lemurcat12
    lemurcat12 Posts: 30,886 Member
    The formula gives me 31.35%. Based on DEXA I'm around 25%. I'm another person who is older (45), and tries to stay fit, although I wouldn't have said I have that much muscle. I do have enough (according to DEXA) that I'd have too low bf at the bottom of the BMI range for my height, though. (I think I'll be happy at 20.5-21, am 22 now, so I'd also have said I'm a person the BMI range works great for.)
  • arb037
    arb037 Posts: 203 Member
    The formula is largely dependent on BMI being accurate. Which for anybody with muscle it is not.
    Formula = 28.74%
    Actual 15-18%
  • rjmudlax13
    rjmudlax13 Posts: 900 Member
    Well, if the formula includes BMI, it's fundamentally flawed from the start.
  • Need2Exerc1se
    Need2Exerc1se Posts: 13,575 Member
    Whoa! No, that wasn't even close for me. Maybe because I'm old and have quite a bit of muscle, but it was over 10% high. And I've had my BF% measured by DEXA scan.
  • Hornsby
    Hornsby Posts: 10,322 Member
    rjmudlax13 wrote: »
    Well, if the formula includes BMI, it's fundamentally flawed from the start.

    Yup.
  • cwolfman13
    cwolfman13 Posts: 41,865 Member
    edited August 2015
    Not remotely accurate for me...it gives me a BF% of 23.96. I'm pretty fit and relatively lean, but not super body builder muscular by any means...my BF% is somewhere around 12-15% per my coaches measurements. I trust those measurements given I have a pretty flat stomach and a 4 pack at this point and no love handles. It's difficult to pinch anything on my body save for the little pouch in the lower abdomen that is preventing me from showing off the last two abs needed for a 6 pack.

    I'm getting oldish but not old @ 40.

    I'm not surprised though...by BMI standards I'm slightly overweight at 25.8
  • nicoleromine
    nicoleromine Posts: 92 Member
    Doesn't work for me either. Gave me 28.7%, and I just had a DEXA scan of 23%.
  • juggernaut1974
    juggernaut1974 Posts: 6,212 Member
    rjmudlax13 wrote: »
    Well, if the formula includes BMI, it's fundamentally flawed from the start.

    Precisely...any decent amount of muscle mass drastically overstates BMI, and therefore will drastically overstate the answer to this formula.

    Add in that if you're of any significant age and keep yourself in shape, it 'punishes' (for lack of a better term) you even more.
  • stormyview
    stormyview Posts: 81 Member
    It seems to be off for women with lower bmi. My BMI is 18.9, and it gives me a body fat percentage of 28. That seems kind of high for someone whose hip bones stick out when standing, with a 24" waist. If I lose two pounds, I'll be considered underweight by BMI, and yet my body fat % is close to 30? Doesn't seem likely. I sure don't look much like pictures of women with that level of body fat!
  • KiltFuPanda
    KiltFuPanda Posts: 574 Member
    As of the middle of last month, I was 388 lbs with a Bod Pod measured bodyfat percentage of 40% (also confirmed via impedance test that same day). I am 6'2", so that gives me a BMI of 49.8.

    If we put this into the formula:

    1.2 x 49.8 + 0.23 x 36 - 16.2

    59.76 + 8.28 - 16.2

    62.04 - 16.2 = 51.84% bodyfat

    I'm not going to call the formula broken (there's gonna be some of us freaks out there), but I would trust direct measurement vs. calculation just based on your height, weight, and age. You can have two people the same height, weight, and age, but with vastly different bodyfat levels.
  • senecarr
    senecarr Posts: 5,377 Member
    I like how everyone in BMI threads rips on how BMI is inaccurate for people with muscle. It's not a good criticism of BMI because
    A. For most of the population, BMI is more likely to underestimate body fat. Based on sampling far more people are within an acceptable BMI but have higher body fat percentage when recommended
    B. Who are these people that have enough muscle to alter their healthy BMI range, but don't already know they're carrying extra muscle?
    For what it is supposed to do, BMI is fine.
  • I_Will_End_You
    I_Will_End_You Posts: 4,397 Member
    It gave me 25.1%. There is no way my bf% is that high.
  • betuel75
    betuel75 Posts: 776 Member
    It says mine is 17.24%. I look like my profile pic. I doubt im 17.24%. Maybe 7.24%..
  • ASKyle
    ASKyle Posts: 1,475 Member
    This formula is just as bad as BMI!

    Formula- 28.05% Latest scan- 24.2%. That's a huge difference on a 5'2 woman.
  • yarwell
    yarwell Posts: 10,477 Member
    I have no idea how BMI can be "inaccurate", as it's weight divided by height squared.
  • ASKyle
    ASKyle Posts: 1,475 Member
    yarwell wrote: »
    I have no idea how BMI can be "inaccurate", as it's weight divided by height squared.

    When people say it's "inaccurate" they're not referencing the formula. They're saying that it is not an accurate indicator of health for many people who exercise, as it does not take into account body fat vs lean mass.

    There's a big difference in health between a woman who is 5'5, 150 and 25% BF, and a woman of the same size who is 40% BF.
  • 970Mikaela1
    970Mikaela1 Posts: 2,013 Member
    My last bod pod said 13.8 ish%. I'm up about 5 pounds from bulking. Formula said I was 25.5%.
  • KiltFuPanda
    KiltFuPanda Posts: 574 Member
    senecarr wrote: »
    I like how everyone in BMI threads rips on how BMI is inaccurate for people with muscle. It's not a good criticism of BMI because
    A. For most of the population, BMI is more likely to underestimate body fat. Based on sampling far more people are within an acceptable BMI but have higher body fat percentage when recommended
    B. Who are these people that have enough muscle to alter their healthy BMI range, but don't already know they're carrying extra muscle?
    For what it is supposed to do, BMI is fine.

    You may have counter-argued yourself in part A. You state that people criticize BMI for being inaccurate, then state that "BMI is more likely to underestimate body fat" - inaccurate is inaccurate, one way or the other. The OP was talking specifically about using BMI to guess your body fat, and I just used my numbers as an example of how inaccurate that formula could be.

    And to answer B, I'd like to put myself up as an example again. I am nowhere near fit levels of body fat, so I don't have much muscle definition, and I get winded easily. For years I honestly thought I was completely out of shape and that I would have to lose weight to less than 250 lbs before I'd be considered healthy. I was convinced that "I'm not fat, I'm big boned" was just an excuse. It took a doctor to "set me straight", so to speak.

    I would consider BMI good as a starting point, but I keep commenting on BMI threads because so many people are focused on getting to a specific BMI and ignoring other factors. If you're going to shoot for a specific goal for your weight loss, go for body fat - that's a more accurate measure of your progress.

  • vismal
    vismal Posts: 2,463 Member
    Merkavar wrote: »
    vismal wrote: »
    Gave me 22.6, not even close.

    Too high?

    Got a bunch of muscles? What do you think you % is?
    Way to high. I'm probably between 11-13 at the moment. I'm not extremely muscular but I do lift weights and am bigger than someone who doesn't.
  • brynnsmom
    brynnsmom Posts: 945 Member
    Man, I came up with 26%. I have no idea what my BF% truly is, but that doesn't seem right for me.
  • rjmudlax13
    rjmudlax13 Posts: 900 Member
    senecarr wrote: »
    I like how everyone in BMI threads rips on how BMI is inaccurate for people with muscle. It's not a good criticism of BMI because
    A. For most of the population, BMI is more likely to underestimate body fat. Based on sampling far more people are within an acceptable BMI but have higher body fat percentage when recommended
    B. Who are these people that have enough muscle to alter their healthy BMI range, but don't already know they're carrying extra muscle?
    For what it is supposed to do, BMI is fine.

    I really don't understand what you are arguing against. Perhaps you are just trolling or something?

    BMI was meant to analyze a large population. It is not a useful tool for an individual. It does not distinguish muscle from fat from bone. How can you defend this as a useful tool for an individual's health? Also, it's used by insurance companies, the military and government (U.S.) to set standards which is idiotic.
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