The above two pictures show me holding a Samsung Galaxy S3 which has a 4.8″ display in my left hand and a Sony Ericsson Xperia X10 which has a 4.0″ display in my right hand. I am holding both phones in a manner that allows me to touch the top opposite corner with my thumb – the position I need for one-handed phone use. The Xperia X10 can be completely enclosed by my hand, when I have a bottom corner resting in my palm it won’t slide down while the Galaxy S3 can slide.
Also one thing I didn’t realise before having the pictures taken is that my posture is quite different when using the two phones. With the Galaxy S3 my wrist is clearly bent and this seems more likely to cause me to have more problems with Carpal Tunnel Syndrome . I haven’t had any serious problems with CTS for the last 2.5 years but I have had minor problems that suggest that I will have to be careful about my posture for the rest of my life.
So it seems that a 4.8″ phone is just too big for ideal one-handed use (grasping the vertical phone from the bottom). As I had CTS problems with my left hand I will try to use my new phone with my right hand as much as possible. Also I can reach further than the width of the phone screen when I grasp it from the side, so for me a size of about 5.2″ would be better than the 4.8″ of the Galaxy S3. It’s quite likely that the Samsung Galaxy Note with it’s 5.3″ screen would be a better device for me to grasp from the side. But the Galaxy Note 2 might be a little too large for me.
Note that I am only considering ways of holding the device that permit full operation. Anything that involves changing position for different uses or occasionally using two hands for a mostly one-hand operation doesn’t count.
The above picture is of me holding a 7″ Android tablet (which I have just returned to Aldi ). When holding it from the sides I can reach more than half the screen with one hand so it seems that the ideal size for a tablet to be held in two hands for me would be 8″ or even a little larger. A tablet larger than that could only be properly used if resting on my lap or a desk – so for me 8″ is the size that differentiates things which can be strictly used as tablets (holding with two hands and using thumbs for input) and things which are more like Netbooks (on desk typing).
Ideal Device Sizes for people based on Height
I am about 190cm tall. If we assume that height and hand size are strongly correlated then we can look at median heights of various age groups and determine what might be a good device size. I am also assuming that everyone wants to have the largest possible device, but some people have other criteria such as the size of their pockets.
For me it’s 8″ tablet, 5.2″ side-grip phone, and 4″ bottom-grip phone. I used data from a chart of the average heights of American boys  and a chart of the average heights of American girls  to determine what size devices might suit children of various ages. Note that before the age of 12 the height of boys and girls is near enough to identical.
|Device||Two Hand Tablet Use||Phone Grasp from Side||Phone Grasp from Below|
|7″ tablet||14yo boy or 17yo girl||noone||noone|
|Galaxy Note 5.3″||10yo||95th percentile 17yo boy||noone|
|Galaxy S3 4.8″||6yo||17yo boy or 95th percentile 17yo girl||almost noone|
|Galaxy S and iPhone 5 4.0″||3yo||10yo||95th percentile 17yo boy|
|iPhone 4 3.5″||noone||8yo||14yo boy or 16yo girl|
One thing that particularly interests me is the educational use of Android devices for children. As few people buy new phones and tablets for young children that largely means that children borrow devices from their parents or are given older phones when relatives no longer need them. So it seems that if all other things are equal then an adult might choose a phone with a 4.8″ display to allow it to be used as a tablet by children in the 6-10 age range.
It seems that the iPhone 4 is a good size for one-handed use by women of average height. By the standards of the people who don’t regard gripping a phone from below as a significant feature the iPhone 4 would be designed for the hand of an 8yo. By any standards all iPhones other than the iPhone 5 were not the ideal size for most adults to use – maybe they are well designed to fit in a pocket while unused. Charles Stross criticised the iPhone because it’s too small to be seen well by people with poor vision , he also makes many other interesting points about the use of phones and I recommend reading his article (and the rest of his blog).
The common tablet size of 7″ seems like it might be ideal for women to hold with both hands, but for men of average height a 7.5″ tablet might be better suited, it sounds like a small difference but it changes button size (good for people with thicker fingers) and allows displaying more data at once (15% greater screen area). Of course if you want to use a tablet on a desk then something much bigger would be better, maybe 12″ or 14″. I think that there is a real market for 14″ tablets that are designed to be carried around the home or office and then used on a table or lap which differs from the tablets that are designed to be more portable.
There is also the use case of holding the phone in one hand while typing with the other which I haven’t considered in this post. I don’t think it’s interesting because in that case almost everyone will find that the limitation is the size of their pockets and the size of an object that can be held to one’s face for a phone call not the size of their hands. I’ve previously written about my search for Geeky jeans and the ability to put a 7″ tablet in my jeans pocket . So I think that pocket size isn’t a phone selection issue for men. The fact that women’s clothing tends to have tiny pockets is another issue, if someone knows of a good analysis of phone size vs pockets in women’s clothes then please let me know.
-  http://etbe.coker.com.au/2010/06/16/carpal-tunnel-getting-better/
-  http://etbe.coker.com.au/2012/12/10/returning-aldi-tablet/
-  http://www.halls.md/on/boys-height-w.htm
-  http://www.halls.md/chart/girls-height-w.htm
-  http://tinyurl.com/3c4kqh5
-  http://etbe.coker.com.au/2012/11/17/geeky-jeans/