A few years ago, we bought a Tanita brand scale at BBB that had body fat percentage sensor on it. Does anyone have any idea how accurate those things are?

They are pretty good, but not as good as the hydrostatic (dunking) or Bodpod tests, or a dexascan, which are all more of a one time measurement that you go someplace to have done and costs a few bucks (or more than a few.) For a snapshot reading, the scales have their limits, as their measurments are based upon body impedance which varies some with hydration. Readings first thing in the morning, when one tends to be deydrated, can be 4-5 points higher in BF% than one taken in late afternoon when one is more fully hydrated, and there can be some day-to-day variations as hydration levels vary some depending activities, weather, etc. Also, changes in medication that effect Water retention can have an effect on it - when my doc took me off of a diuretic BP med a few years ago, my weight didn't change, but there was an almost immediate jump in the BF% reading. That said, if used it consistently to average out the daily variations, I have found that they correlate quite well with the hydrostatic tests that I have had done.

One other source of error in them comes from where they measure your impedance and where you store your fat. Typically the scales measure between your bare feet, so those who store their fat in their legs and butt (pear shaped) will read a somewhat higher BF% than those who store their fat around their abdomin (apple shaped.) Some gyms or trainers may use a device that you hold in your hands, which will read the opposite as it is measuring more of the abdomin; there are some scales out there that have a hand held attachment that takes a reading from both the feet and hands to correct that error.

If total accuracy of the number is most critical, or as a periodic calibration of scale readings, then certainly go get one of the better snapshot measurments done, but the scales are a useful tool for monitoring things on a daily basis if you keep their shortcomings in mind.

They are pretty good, but not as good as the hydrostatic (dunking) or Bodpod tests, or a dexascan, which are all more of a one time measurement that you go someplace to have done and costs a few bucks (or more than a few.) For a snapshot reading, the scales have their limits, as their measurments are based upon body impedance which varies some with hydration. Readings first thing in the morning, when one tends to be deydrated, can be 4-5 points higher in BF% than one taken in late afternoon when one is more fully hydrated, and there can be some day-to-day variations as hydration levels vary some depending activities, weather, etc. Also, changes in medication that effect Water retention can have an effect on it - when my doc took me off of a diuretic BP med a few years ago, my weight didn't change, but there was an almost immediate jump in the BF% reading. That said, if used it consistently to average out the daily variations, I have found that they correlate quite well with the hydrostatic tests that I have had done.

One other source of error in them comes from where they measure your impedance and where you store your fat. Typically the scales measure between your bare feet, so those who store their fat in their legs and butt (pear shaped) will read a somewhat higher BF% than those who store their fat around their abdomin (apple shaped.) Some gyms or trainers may use a device that you hold in your hands, which will read the opposite as it is measuring more of the abdomin; there are some scales out there that have a hand held attachment that takes a reading from both the feet and hands to correct that error.

If total accuracy of the number is most critical, or as a periodic calibration of scale readings, then certainly go get one of the better snapshot measurments done, but the scales are a useful tool for monitoring things on a daily basis if you keep their shortcomings in mind.

This is GREAT information, thank you!!