The misleading thing about the term “Retina” is that it varies between iPhone (326 dpi), iPad (264 dpi), and MacBook (220 dpi). Basically they use it to mean double the regular resolution/dpi. It’s a good-enough term because of the varying distance these devices would typically be from your eyes. The dpi of the iPad Mini is 163, which means that the retina version of the Mini will have the same dpi as the retina iPhones (326).

@Sean
There isn’t a rule for this but there is logic in starting small and scaling up rather than vice versa. Lets say you need to support mdpi (non-retina), hdpi, xhdpi (retina), xxhdpi…so the best option is to create your baseline as mdpi because Photoshop based vector files scale up much more smoothly than scaling down. If you create at xhdpi (retina) then you are making a lot more detail in that size and when you scale down you are trying to pack the detail into a smaller size which can result in artifacts or missing pixels. This even applies if you are using vector elements like custom shapes and layer styles. – If you start from mhdpi and scale up the elements will actually adjust the detail and add more rather than trying to fit detail into smaller assets.

@Bretton
Retina is rather misleading in multiple ways because the iPhone 4S and iPhone 5 have different results even though they are both Retina. If you use a converter to find the retina version of something then that applies to iPhone 4S and older where as the iPhone 5 will automatically be different regardless of them bothing being 326dpi. This is also irrelevant though. The iOS SDK actually provides pixel resolutions for each size of the iPhones and iPads include landscape vs portrait and retina vs non-retina. This makes a converter unnecessary for iOS design.

iOS design is MUCH easier than Android…I have a love hate relationship with Android because as a User I love that vast amount of options…as a Designer, I hate it. :)

‘Retina’ is a somewhat loose term:
Retina iPhones = 326dpi (roughly equivalent to xhdpi)
Retina iPads = 264dpi (roughly equivalent to hdpi)

I know this article is 8 months old, but it’s got a lot of Google juice and appears at the top of almost any Android resolution search. A fix here would probably save a lot of headaches.

Thanks for the article and the tool.

I was wondering if you guys start in retina (I imagine so since your gui .psd files are usually retina?). Some Designers tell me I should actually scale up, rather than down?

https://play.google.com/store/apps/details?id=com.useit.software.android.densityconverter

Also available in iphone:

http://itunes.apple.com/es/app/conversor-pixel-densidad/id566581570?mt=8