# How fat do you have to be to float withot effort? **URL:** \ **Category:** Factual Questions\ **Created:** [November 27, 2013, 5:50pm UTC](https://boards.straightdope.com/t/how-fat-do-you-have-to-be-to-float-withot-effort/674933 "2013-11-27T17:50:19Z")\ **Posts on this page:** 13\ **Page:** 2
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [November 29, 2013, 2:57pm UTC](https://boards.straightdope.com/t/how-fat-do-you-have-to-be-to-float-withot-effort/674933/21 "2013-11-29T14:57:29Z")
I’ve always been overweight, even obese and always floated easily. Now I am down to slightly overweight (BMI = 27) and I still float readily, but especially in the ocean. I once bathed in the dead sea and that is a real experience, since you can sit in the water with 30% of your body above water. Getting out is also interesting since you feel no wind (the water is saturated and difficult to evaporate) and you take a fresh water open air shower and instantly start to chill. ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [November 29, 2013, 8:31pm UTC](https://boards.straightdope.com/t/how-fat-do-you-have-to-be-to-float-withot-effort/674933/22 "2013-11-29T20:31:32Z")
> [@LinusK](#): > > My swimming teacher in HS insisted “everybody” floats, when she tried to teach the deadman’s float. Didn’t work for me, unless I treaded water at least a little bit. Without my lungs completely full of air, I sink like a stone. I taught swimming at a Boy Scout summer camp for five summers, and I mostly agree with your teacher, but I’d qualify it to say _almost_ everybody can float. Lie back in calm water, spread your arms, breathe slowly and calmly, and fill your lungs completely each time. 95% of the kids I taught could float this way without moving their arms or legs. There were always a few, though, who couldn’t, regardless of physique. ---
**Author:** ![Becky2844](https://avatars.discourse-cdn.com/v4/letter/b/91b2a8/32.png) [@Becky2844](https://boards.straightdope.com/u/Becky2844)\ **Post date:** [November 30, 2013, 1:58am UTC](https://boards.straightdope.com/t/how-fat-do-you-have-to-be-to-float-withot-effort/674933/23 "2013-11-30T01:58:21Z")
> [@rhubarbarin](#): > > I float almost effortlessly on my back. I’m very thin (BMI 17) but all my fat is in my hips, so they float, and my upper body is so light that it seems all I need to do is breathe to keep it buoyant. I’m pretty sure could sleep in the water on my back. This is the way I am. I don’t need a “float” to float. When I try to swim underwater I drift back up to the top. My younger son, though, almost didn’t pass a lifeguard test because he had to tread water to keep from sinking. Neither of us overweight. ---
**Author:** ![Becky2844](https://avatars.discourse-cdn.com/v4/letter/b/91b2a8/32.png) [@Becky2844](https://boards.straightdope.com/u/Becky2844)\ **Post date:** [November 30, 2013, 2:11am UTC](https://boards.straightdope.com/t/how-fat-do-you-have-to-be-to-float-withot-effort/674933/24 "2013-11-30T02:11:47Z")
I’ve heard this has something to do with bone density, but IDK. Just realized we’re in General Questions! I’m sorry, I don’t have a cite. ---
**Author:** ![Sleel](https://avatars.discourse-cdn.com/v4/letter/s/73ab20/32.png) [@Sleel](https://boards.straightdope.com/u/Sleel)\ **Post date:** [November 30, 2013, 4:07am UTC](https://boards.straightdope.com/t/how-fat-do-you-have-to-be-to-float-withot-effort/674933/25 "2013-11-30T04:07:53Z")
I’ve never been able to float on my back without my legs sinking and eventually dragging the rest of my body down. I always have to do at least a little flutter with my hands near my hips or a tiny kick every once in a while to keep my legs up. Even at my fattest during the few years my weight ballooned from “normal” to “pretty damn fat”, my legs were dense enough to cause problems with floating. It’s not technique either, because I’ve been swimming since literally before I have solid childhood memories. I’m utterly comfortable in the water, I just can’t stop moving at least a little, or I’ll sink. So for me, the answer is: fatter than I’ve ever been and fatter than I’ll ever allow myself to become again. ---
**Author:** ![Boberoo](https://avatars.discourse-cdn.com/v4/letter/b/db5fbb/32.png) [@Boberoo](https://boards.straightdope.com/u/Boberoo)\ **Post date:** [November 30, 2013, 11:11am UTC](https://boards.straightdope.com/t/how-fat-do-you-have-to-be-to-float-withot-effort/674933/26 "2013-11-30T11:11:51Z")
Super long and skinny male- I used to hang out at the bottom of the pool. Drove my mom nuts playing “newt”. Even at Magic Mountain, on that spinning room, when the floor dropped out and everyone clung to the wall by centrifugal force, I would slide down with the floor. Freak of nature, I guess. I was finally able to float in the Sea of Cortez, down in Baja Mexico. ---
**Author:** ![SciFiSam](https://avatars.discourse-cdn.com/v4/letter/s/47e85d/32.png) [@SciFiSam](https://boards.straightdope.com/u/SciFiSam)\ **Post date:** [December 2, 2013, 10:35am UTC](https://boards.straightdope.com/t/how-fat-do-you-have-to-be-to-float-withot-effort/674933/27 "2013-12-02T10:35:36Z")
> [@naita](#): > > With a height of 186 cm and a BMI at the very lowest end of normal I used to have negative buoyancy unless my lungs were filled to the max. If I let my breath out I would sink like a thing with significant negative buoyancy. > > I’m now more comfortably in the normal BMI range, though still skinny by most standards, and although I haven’t really thought to test my buoyancy lately I suspect I now float just fine, so you “Most people” is probably accurate. I just wanted to make it clear that really skinny people sink. No, they don’t, not necessarily anyway. I’ve always floated like a rubber duck, even when my BMI was 17. And some overweight people find floating very difficult. Weight may be a factor, but it’s not the only one. ---
**Author:** ![GameHat](https://avatars.discourse-cdn.com/v4/letter/g/ed655f/32.png) [@GameHat](https://boards.straightdope.com/u/GameHat)\ **Post date:** [December 2, 2013, 12:35pm UTC](https://boards.straightdope.com/t/how-fat-do-you-have-to-be-to-float-withot-effort/674933/28 "2013-12-02T12:35:06Z")
back in high school, when I was in pretty good shape (soccer and basketball teams) - I was probably 5’10, 170 lbs. I would float in a swimming pool when I held my breath, but I could reliably sink to the bottom, no effort other than exhaling, by emptying my lungs. ---
**Author:** ![snowthx](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snowthx/32/10660_2.png) [@snowthx](https://boards.straightdope.com/u/snowthx)\ **Post date:** [December 2, 2013, 7:33pm UTC](https://boards.straightdope.com/t/how-fat-do-you-have-to-be-to-float-withot-effort/674933/29 "2013-12-02T19:33:01Z")
My wife insists that anyone can float, and each time she tries to show me with my body, I prove it false. She keeps saying I am “doing it wrong”, but like others here, my legs end up dragging me down. There is no way to keep my legs floating without some effort. I can float fine if I put an inflatable ring under my ankles, however. I am about 5 11 with BMI about 26. ---
**Author:** ![Aji\_de\_Gallina](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aji_de_gallina/32/260_2.png) [@Aji\_de\_Gallina](https://boards.straightdope.com/u/Aji_de_Gallina)\ **Post date:** [December 2, 2013, 7:40pm UTC](https://boards.straightdope.com/t/how-fat-do-you-have-to-be-to-float-withot-effort/674933/30 "2013-12-02T19:40:52Z")
I’m 1.83m (6’) tall and even at my fattest (110kg - 240lb) I wouldn’t float if I let all the air out of my lungs and kept still. Even at my skinniest (70kg - 155lb) I’d float with my lungs fully inlfated. ---
**Author:** ![Hampshire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hampshire/32/4887_2.png) [@Hampshire](https://boards.straightdope.com/u/Hampshire)\ **Post date:** [December 2, 2013, 9:19pm UTC](https://boards.straightdope.com/t/how-fat-do-you-have-to-be-to-float-withot-effort/674933/31 "2013-12-02T21:19:35Z")
> [@DSeid](#): > > So all this tells us the GQ answer seems to be “it depends …” > > Interestingly the biggest difference might not be how much fat, or even where the fat is, or even how much muscle. Skeletal variation probably matters more. Bones are the most [dense human tissue](http://www.scrollseek.com/training/densitiesofdifferentbodymatter.html) by far. Type Avg Density Value (g/ml) Blood 1.0428 g/cm3 Bone 1.7500 g/cm3 Fat 0.9094 g/cm3 Muscle 1.0599 g/cm3 Since water is what… 1.0 g/cm3 your combined density would have to be \< 1.0 g/cm3 in order to float. That would include the density of the air in your lungs. Looks like the more fat you have on you is going to be to your advantage as well as holding a good breath of air. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [December 2, 2013, 9:34pm UTC](https://boards.straightdope.com/t/how-fat-do-you-have-to-be-to-float-withot-effort/674933/32 "2013-12-02T21:34:39Z")
Yes, more fat an advantage. And less thick or dense bones or a narrower frame. Or a build that is more thorax with bigger lung capacity and more residual lung volume. And less muscle. (Of course muscle mass follows skeletal structure some too.) Yes water is 1.0. The net (in fresh water) has to be less than 1.0 to float. You need 7 additional volume units of fat to offset one additional volume unit of bone, not counting the extra muscle that covers and carries that bone. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [December 2, 2013, 9:46pm UTC](https://boards.straightdope.com/t/how-fat-do-you-have-to-be-to-float-withot-effort/674933/33 "2013-12-02T21:46:49Z")
5’10" bouncing between 225 and 250lb, I always had problems staying down. Very annoying, especially snorkelling in salt water, I wanted to float up very quickly. I was trying to get pictures of fish underwater and kept floating away unless I was kicking. Of course, that’s salt water, and a mask and lungs full of air. At about 215lb and swimming pool I had no problem staying down for extended periods (25m underwater, or for underwater hockey) altough I did tend to drift upwards. With a thick neoprene wet suit during scuba training I had to wear a fairly hefty weight belt, about 15lb or more IIRC. [Previous page](https://boards.straightdope.com/t/how-fat-do-you-have-to-be-to-float-withot-effort/674933.md?page=1)