A couple of years back when working on migrating a design to the Nokia E60 I ran into an interesting problem that resulted in my questioning something that I’d taken as fact for a number of years. Exactly how big is a pixel?

Ever since I can remember (circa the early 90′s) the standard measurement was roughly 72 to 96 pixels per inch. This of course was typically based on display sizes averaging 17 inches diagonal with screen settings of around 800 x 600 pixels to 1024 x 768 pixels. Of course, some displays were capable of displaying many more pixels – but this was a decent yardstick to go by for a number of years. Recently however things have started to change significantly – but we’ll get to that in a bit.

Getting back to my Nokia E60 problem. This device has a screen size of 352 x 416 pixels which was exactly double that of my existing design of 176 x 208 pixels for the Nokia 6630. At first I was really excited about what I might be able to add to my original design with all of these extra pixels – after all, this device has double the screen size, right?

Well, not exactly. Yes, the screen size was double – but the actual display size was about the same (roughly 2 inches diagonal) which required all font and image resources to be scaled up by 200% in order for the design to be useable. For example, the original design had a bitmap font with a height of 8 pixels which when displayed on the E60 was half the visible height of the same font displayed on the 6630 – which of course was completely illegible. Again, the solution was fairly simple – scale the font and all resources by 200%.

Now I hear you saying to yourself “No problem – I’ll simply scale all my resources appropriately!”. Well, it’s not quite that simple any more as Barbara Ballard recently pointed out. Today mobile designers now have to deal with screen sizes ranging from 128 x 128 pixels to 320 x 480 and higher, with pixel densities ranging anywhere from 110 pixels per inch all the way up to (and over) 193 pixels per inch.

The reality today is that mobile designers are required to be much more aware of the screen size and display variants they are being asked to design for. Information about screen sizes is typically easy to find – but data on display sizes (the actual physical screen size) is much rarer. Lately there has been some interest in seeing this information added to device data initiatives such as WURFL, DeviceAtlas and even Adobe’s Devce Central, but it’s largely going to fall to the community to provide much of this information until the device manufacturers are motivated enough to begin publishing it.