I’m reading about the new Amazon “Large Screen” Kindle and some reviewers are wondering if the device is too big. The Kindle 2 is about half the size of a sheet of paper and the new Kindle DX is about the size of an 8 1/2” x 11” sheet of paper. Since when is a sheet of paper too big?

So, if you happen to be developing a portable device how do you determine its appropriate size?

Way back in 1984 the first Motorola DynaTac cell phone was compared to a brick, in both size and weight. Today’s Razr cell phones are about 4” folded and 7” unfolded length wise and about 2” wide. I have a slider phone (not a Morotola) that has a slightly smaller screen than a Razr's but also happens to be 4” long docked and about 5 ¼” long extended and a little less than 2” wide. So it seems that the a good size goal for a basic cell phone may be the U.S. Dollar bill, as its 6.14 inches long and 2.61” wide or 155.956 mm long by 66.294 mm wide. Folding it in half reduces its size or overlapping sections like slider phones also make it more compact.

Well what about smart phones like the Apple iPhone or Blackberry? Well, take your basic 3” x 5” index card and design away. Most smart phones will easily fit onto an index card of this size (most are a little smaller actually).

If you are looking at designing something a little bigger, say a UMPC (Ultra Mobile PC)? Well a 6” x 9” wire bound steno pad seems to be the standard size.

I seem to think that maybe an 8.5” x 5.5” device might be a good size. Basically it’s the same as half of a sheet of paper. You might be able to get a screen size of about 8.5” diagonal. This is a little bit bigger than some of the UMPC’s on the market today, and provides some room for a larger screen and keyboard.

So, is using products that we seem to use every day to as a guide for new products? Well it seemed to work well for Herman Hollerith, who designed the first punch card system, somewhat based on the size of U.S. currency available at that time , which were a little larger than today’s currency, and the control cards for 1880 area textile looms. It could also be coincidental that the original iPod was about the same size as a deck of cards.