How accurate is it to say that the length of your outstretched arms from fingertip to fingertip will be the same as your height? I have heard somesay say that her son should be taller because his “wingspan” is bigger than his height. To me, that immediately disqualifies the relationship but I was wondering if there was a real body proportion bell curve type relationship for this.
When I took a physical anthropology course, one of the classroom demonstrations was for everyone to measure the distance between their outstretched arms and compare it to their height. The two measurements were very close to each other for everyone in the class. It didn’t seem to be affected by body type or gender.
My armspan is actually slightly more than my height - about 2 inches more. A classmate of mine did a study of people in my school once, and the agreement was pretty good, if I remember right. Again, it didn’t seem to be related to gender or body type.
Michael Gross, a swimmer for (West) Germany known as the albatross, was just over 2 metres tall but had a wingspan of 2.27 metres.
Ian Thorpe of Australia is also supposed to have had a long wingspan relative to his body length, giving him a disproportionately long stroke.
How accurate do you need it to be? In most humans, the “wingspan” is close enough to body length for the saying to work - I doubt the diff. is more than 5 cm., even for people with unusual proportions (my fiance has longer than normal arms, so his wingspan is longer than his height, too.) If you want to use it as rule-of-thumb when measuring things on the fly - say, a length of string from your fingertips to the middle of your breast will be roughly one meter (a bit more than a yard) or similar things, then 5 cm. or less won’t matter.
Do you want to classify somebody as ape instead of human because his arms are longer than his body height? 
I think you’d need more of a difference there (And of course, several other, more obvious signs - opposable thumb? Upright walk? Able to talk, or only grunts?)
Do you want to know whether somebody has different proportions than the standardized man/woman, eg when buying clothes, chairs etc.? Then measure directly with a tape-measure, and try things on.
I’m 6’2" and my wingspan is about 6’5"
I have this theory
People with slightly longer arm spans than their height tend to hang around on SDGD
About 40 years ago, we were all measured, I was the freak and automatically thought that when they get around to inventing the Internet I’ll find a few other Orang Utangs.
Here’s one available study showing it’s fairly accurate Size of a Human: Body Proportions - The Physics Factbook
It’s a tiny one done by students, and most of the hits on google seem to be for teaching projects, so it’s accurate enough to be useful in such a setting.
I on the other hand have a very long back so my measurements are:
height 186cm (6’ 1")
armspan 175cm (5’ 9")
I believe my growth curve as a kid indicated 175 would be my adult height, so I suppose I’m some sort of freak. 
My dad got polio in one of his legs when he was very young, and they had to stop the growth in both his legs so he wouldn’t walk around all crooked-y. As a result, he’s got a very long torso and short little legs. He’s about 5’8". I’m almost 6’3". Our wingspans are almost identical. I’ve long thought that we’d be the same height if it weren’t for his disease because of this little test.
I learned this little factoid in drawing class. It’s true for all practical purposes. The one that kills me is the fact that your foot is about the same length as the distance between your inner wrist and inner elbow.
Also, your hand is about as long as your face and your body is about 7 heads high.
I just saw a thing on chimpanzees and learned that their arm span is about 1.5 times their height, which forces them to walk on their knuckles.
Don’t know if this is painfully obvious, but the west way to test this is to stand next to a wall. Place your hand flat on top of your head so your finger tips touch the wall. Hold that hand there. With your other hand, reach towards the floor. Wow, it just about exactly touches the floor!
I use this factoid all the time to measure the dimensions of various things.
Not if the practical purpose is me building a door and using my armspan to judge the necessary height.
The span-equals-height rule is generally true, within an inch or two. It’s useful for painters and tailors, but only occasionally so for the rest of us. There are many exceptions, and you don’t have to look far to find one. If you need to quickly measure a piece of rope close to your height, or half that, it’s useful to know the length of your span.
I’m 6’ 4", so I can measure roughly 6 or 3 feet without a tape measure. It’s nice for reloading my grass trimmer or hanging my big extension cord in 6 foot loops.
My wingspan is an inch or two longer than my height, using the hand-on-the-wall method described above (I’m sure that looked strange to anyone who was walking past my office while I was doing it). That would explain why I’ve always had difficulty buying shirts that fit my shoulders but aren’t too short to reach my wrists. I tend to prefer 3/4 length sleeves on blouses for just that reason.
Not much to add except that my height is 5’11" and my wingspan is about 6’5".
Why yes, I would like a banana. How nice of you to ask. 
I found out when I was learning how to do rock climbing that I’ve got a longer than average wingspan. My regular climbing partner was a friend of mine who worked at the climbing wall. He set a route that was for tall people, making all the holds almost impossible to get to even if you stretched, or a requiring a dynamic move, for anyone who was under about 6 feet tall. I only had trouble with one or two holds and they were a stretch for him too.
He thought that was weird, since he’s about three inches taller than me, standing a little over 6 feet, so we measured my wingspan by standing chest to chest with arms outstretched. Even though I’ve got paws for hands, my arms were so much longer that I was able to close my fingers over the ends of his fingers. His fingers only came to about mid-palm on me.
(Seriously, my fingers are short and stubby compared to the size of my palms; they should be about a joint and a half longer for normal proportions. My 5’1" fiancee has fingers that are the same length as mine, though mine are much thicker. I can’t wear her thumb ring even as a pinky ring.)
t’is true, and I have a friend who has bigger feet, but shorter arms than me 
As a sidenote, having a “wingspan” longer than your height MAY be a symptom of Marfan Syndrome.
See here for more symptoms and see if anything else on the list rings true for your friend’s son: Marfan Syndrome - What Is Marfan Syndrome? | NHLBI, NIH
or this page for more details on the condition: http://www.marfan.org
While it is not a very common condition, Marfan Syndrome can be very serious. If it is left undiagnosed, a lot of people with the syndrome die suddenly from aorta dissection. That’s how Jonathan Larson, the guy who wrote the Broadway show “Rent”, died.
So, I just figured this sidenote was worth mentioning in case someone out there might benefit from it.