For up-to-date information see:
Android (4.1) Icon Size Guide Made Simple

Android runs on many different hardware platforms with different screen sizes and pixel densities. For this reason it is a little more complex to create icons for compared to something like the iPhone, as depending on the platform your App is aimed at, you may need several different sizes for your icon design.

This guide should help you determine the Android App Launcher Icon Sizes required for your App.

Android  Launcher Icon Sizes

A launcher icon graphically represents your App on the application home page or launcher window.

Your icons should be:

• 36×36 for low-density screens (ldpi)
• 48×48 for medium-density screens (mdpi)
• 72×72 for high-density screens (hdpi)
• 96×96 for extra high-density screens (xhdpi)

Typically the Android App Icon sizes listed above will represent the maximum available space and it is advisable to include some padding within the specified area to allow for effects such as drop shadows.

Android Market High Resolution Icon

When you submit your App to the Android Market you will need to include a high resolution version of your launcher icon, for use in various places throughout the Android Market.

• 512×512 for Android Market

Other Android App Icon Types & sizes

As well as the actual App Launcher Icons you may also need to design various interface icons for your application. What follows is a short summary for all the interface icons you should need for Android 3.0 + applications.

Action Bar Icons (Android 3.0 and later)

Action Bar Icons are used to display individual actions within the action bar menu. Typically they are simple 2D flat, grayscale images in transparent PNG format.

• 18×18 for low-density screens (ldpi)
• 24×24 for medium-density screens (mdpi)
• 36×36 for high-density screens (hdpi)
• 48×48 for extra high-density screens (xhdpi)

If you are following the default ‘Holo Light’ or ‘Holo Dark’ themes the icons should use a specific colour palette for the icon. The icon shape should be ‘hollow’ with no colour fill within the icon design. The background and ‘fill’ area should be transparent.

• Holo Light – Icon Colour:  #333333 (60% opacity)
• Holo Dark – Icon Colour:  #ffffff (80% opacity)

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Status Bar Icons (Android 3.0 and later)

These icons provide notifications in your App status bar.

• 18×18 for low-density screens (ldpi)
• 24×24 for medium-density screens (mdpi)
• 36×36 for high-density screens (hdpi)
• 48×48 for extra high-density screens (xhdpi)

As with all icons you can vary the height and width of non-square icons designs to ensure a constant visual weight to the surrounding icons. As with the Action Bar Icons the icon shape should be ‘hollow’ with no colour fill within the icon design. The background and ‘fill’ area should be transparent.

• Icon Fill Colour: #ffffff
• Background and inner content: Transparent

Dialog Icons (Android All versions)

Dialog icons are used in pop-up boxes designed to prompt users for interaction. They use a light gradient colour to stand out against a dark background.

• 24×24 for low-density screens (ldpi)
• 32×32 for medium-density screens (mdpi)
• 48×48 for high-density screens (hdpi)

When creating a Dialogue icon, like those previously listed, they must be created in a transparent (32bit) PNG format. Taking the 32×32 size as an example, 1 pixel of padding around the image is ideal, although you can cross this with anti-aliasing on non-square icons shapes.

The correct lighting effects for creating consistent Android Dialogue Icons follow, these instructions assume familiarity with Adobe Photoshop:

• Start with a white Icon shape with transparent cut-outs where required
• Gradient Overlay:
  • Angle 90 degrees
  • Bottom colour R223 G223 B223
  • Top colour R249 G249 B249
  • Bottom colour location 0%
  • Top colour location 75%
• Inner Shadow:
  • Fill colour Black
  • 25% opacity
  • Angle -90 degrees
  • Distance 1 pixel
  • Size 0 pixels

List View Icons (Android All Versions)

List view icons are used in the, wait for it, ‘List View’ such as in the ‘Settings’ application. At first glance these icons look aesthetically very similar to the Dialog icons but use slightly different shadow effects so be careful not to confuse the two if you want to keep your icons consistent.

• 24×24 for low-density screens (ldpi)
• 32×32 for medium-density screens (mdpi)
• 48×48 for high-density screens (hdpi)

The main difference between the Dialog and List View Icons is the background and icon ‘cut-outs’ which are black. The full list of effects can be found below:

• Start with a white Icon shape with black cut-outs where required, on a black background
• Gradient Overlay:
  • Angle 90 degrees
  • Bottom colour R223 G223 B223
  • Top colour R249 G249 B249
  • Bottom colour location 0%
  • Top colour location 75%
• Inner Shadow:
  • Fill colour Black
  • 57% opacity
  • Angle 120 degrees
  • Blend mode normal
  • Distance 1 pixel
  • Size 1 pixel
• Background: Black (#000000)

Android provide a fairly comprehensive set of Icon Design guidelines for Android Icons but they are split over several pages so I hope having most of them here on one page is useful. I will endeavour to follow up with another post on Android 2.3 Icon sizes at a later date.

Official Android Icon Design Guidelines