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Thread: Body Fat %- am I doing my math correctly? page

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    Saoirse's Avatar
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    Body Fat %- am I doing my math correctly?

    Primal Fuel
    So the other day, I stepped on a friend's scale that supposedly measures body fat %. It said that 34% of my weight (135lb) is body fat. 135X.34=47.5 lb! Is that right? So, if I wanted to get down to only 15% body fat, I would have to drop 35 lbs, right? Here's my math:
    135-47.5=87.5 (lean weight?)
    87.5*1.15=100.625 (weight with added 15% body fat?)

    Okay, so i know this doesn't take into consideration an increase in weight due to increased muscle mass. But as far as muscle mass goes, I'm really not that skinny now. So I'm thinking that my math logic must be off. Can anyone help?

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    peril's Avatar
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    Your maths is good. I just wouldn't believe that a scale could measure my body fat percentage

  3. #3
    Saoirse's Avatar
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    thanks. I think that the scale must be wrong. If I weighed just 100 lbs, I would have a BMI of 17.2. My goal weight is around 115-120, though I'm more concerned about how I look and feel than what I weigh.

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    I wouldn't trust a scale to give anything like an accurate measurement of bf percentage. If you can get booked in a bod pod you can get a very accurate reading, but if you can find a measuring tape, this is about the best you could do. Hope it helps. Your scale might be reading high so, you just might like this better anyway.

    http://www.scientificpsychic.com/fitness/diet.html

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    A scale CANNOT measure bf. At best it can do some bullshit like the BMI (which is mostly meaningless anyway).

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    Hoooowww taaaaalllll aaaare yoooouuuuu

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    A scale can measure body fat percentage by using impedance, which is only accurate if you are well hydrated

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    Tanita has a scale which says it can measure bodyfat percentage. It does this by impedance. Bone and muscle (LBM) have low impedance, fat has higher impedance. Problem is, the scale only measures the current flow from one leg to the other, and does not account for hydration. Your BF% in your upper body will not betaken into account with a Tanita scale.

    If you carry a lot of your fat in your hips/thighs---the bf% it gives will not be accurate. Also...if you're a little dehydrated, as in the morning...your bf% can read 7-10% higher, than the rest of the day. Just sayin'....

    ETA: Take your weight in the morning---take your bf% in the afternoon.

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    I've got a salter bioimpedance scale. I know its a load of rubbish, but it is nice to have something to go on if you are weighing yourself regularly (eg, my bf has dropped by 3.5% since I got it 6 months ago) Interesting kuno about it being higher in the morning, cause that is when I measure most the time, ie after having a cuppa tea and going to the loo and then having a shower. When I got weighed on the gym Tanita scales the amount was MUUUUUUUUUCH higher. Hence I dont really take a hell of a lot of notice of any of them I just want to look smoking in a bikini some time and I dont need a body fat measurement to tell me that I look good (assuming that will happen sometime)

  10. #10
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    With the scales, as long as you use the same one each time and at the same time of day it will give you an idea of whether or not you are losing BF. No, it won't be 100% accurate, but it is easy to do We had one that was pretty close to being accurate. I went into a Bod Pod and then the next day used our scale (after the shower so there is better contact with the electrodes) the scale was just a little over 1% off. That was close enough for me to know I was getting a fairly good idea of my BF%.

    The one we had also measured hydration levels, so if my hydration level was low and my BF% was higher than normal, I knew why. It was nice until the kids got a little primal in the bath tub and flooded the floor, now it doesn't work at all...lol

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