Did you know arm span ( also known as wingspan or reach ) is approximately equal to height?
How to calculate arm span
We tested this against a wall using chalk to mark our reach and then standing next to the wall to see if it matched our height. You should measure from fingertip to fingertip and not have a flat hand, as in this photo.
We found my 6-year-old's arm span did equal his height, and my 4-year-old was a little taller than hers.
What is the ape index?
Ape index is the ratio of arm span relative to their height. So my little boy had an ape index of 1.
An arm span greater than height is thought to be advantageous in some sports, such as swimming, as longer arms may give greater propulsion. A shorter arm span is useful for weight lifters as they don't have to lift the weight as high.
How to calculate ape index
Ape Index - Method 1
Wingspan / Height
If ape index is greater than 1, wingspan is greater than height. If ape index is less than one height is greater than wingspan.
Ape Index - Method 2
Wingspan - Height
Ape index calculated this way is either a positive or negative number.
Can you work out your ape index or arm span?
Grab the instructions below. I have a basic investigation instruction sheet and also a slightly different format using a question.
More human body science ideas
Can you work out how many feet tall you are?
Make a model of a heart or a brain model.
Or, for little ones, try some of these great preschool science ideas.
Last Updated on July 31, 2023 by Emma Vanstone
Emma says
My little ones love this too! Great fun. I didn't know it had a proper name though! (And apparently your foot is the length of your forearm too.)
ScienceSparks says
I keep meaning to try that one!
rscionka says
My fore arm is 3 inches longer than my foot and my arm span is 5 inches greater than my height... ape arms...
HELEN says
interesting stuff! I will be checking out our ape index...I suspect that the males of the family have longer arm spans than height....good for reaching glasses from the top shelves!
ScienceSparks says
Ha ha, good point!
Jodi says
This is so simple but a really fun idea. Thanks for the inspiration.
Heather twinkl says
Did not know that! Am now going to spend the next hour with my boys on this!
Itchy says
I herd this along time ago on Braniac I think so have added their URL! but when I checked it my Span of my Arm's is 2-3 inches LONGER than my Height so Wife laughed and said that I am an Ape!
Maria says
If your arm length is significantly longer than you are tall it could be d genetic disorder called Marfan syndrome.
John Lukeward says
I have an arm span of 76" my height is 65" a difference of nearly a foot. Is my arm span too long?
Adam says
Well, that means that you should've reached that height,and there might have been health problems that have caused the decrease in height.
Mario says
Wouldn't it only be a decrease in height if John had once been more than 65" tall?
Lisa says
My 6 year old son is short in stature anyway but his arm span is even less than his height by 4/5 cm. Will this rectify and if not will it cause him problems when he gets older?