Size and weight are big decision factors when you are trying to find the ideal camera for your needs.
In this section, we are going to illustrate the Sony A550 and Sony A390 side-by-side from the front, back and top in their relative dimensions. Sony A550 has external dimensions of 137 x 104 x 84 mm (5.39 x 4.09 x 3.31″) and weighs 632 g (1.39 lb / 22.29 oz) (including batteries). Sony A390 has external dimensions of 128 x 97 x 86 mm (5.04 x 3.82 x 3.39″) and weighs 549 g (1.21 lb / 19.37 oz) (including batteries).
Below you can see the front-view size comparison of the Sony A550 and the Sony A390. Sony A390 is 9mm narrower and 7mm shorter than Sony A550 but it is also 2mm thicker.
Here is the back view size comparison of the Sony A550 and Sony A390.
Now lets look at the top view comparison of Sony A550 and Sony A390.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Also keep in mind that body weight is not the only deciding factor when comparing two interchangeable camera bodies, you also have to take into account the lenses that you will be using with these bodies. Since both Sony A550 and Sony A390 have the same Sony/Minolta Alpha lens mount and APS-C sized sensors, lenses will not be a differentiator on total size of the system.
Weather Sealing
Unfortunately neither the Sony Alpha DSLR-A550 nor Sony Alpha DSLR-A390 provides any type of weather sealing in their bodies, so you have to give extra care especially when you are shooting outdoors. If weather sealing is a must-have feature for you, check these sections: Top DSLR Cameras with Weather Sealing
LCD Screen Size and Features
Sony A550's 3.00" LCD screen is slightly larger than Sony A390's 2.7 screen.
Both cameras feature
Tilting screens where you can change the angle of the screen to make it easier to shoot from waist or over-the-head levels.