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 Nikon D3100 and Sony A380 side-by-side from the front, back and top in their relative dimensions. Nikon D3100 has external dimensions of 124 x 96 x 75 mm (4.88 x 3.78 x 2.95″) and weighs 505 g (1.11 lb / 17.81 oz) (including batteries). Sony A380 has external dimensions of 128 x 97 x 71 mm (5.04 x 3.82 x 2.8″) and weighs 519 g (1.14 lb / 18.31 oz) (including batteries).
Below you can see the front-view size comparison of the Nikon D3100 and the Sony A380. Nikon D3100 is 4mm narrower and 1mm shorter than Sony A380 but it is also 4mm thicker.
Here is the back view size comparison of the Nikon D3100 and Sony A380.
Now lets look at the top view comparison of Nikon D3100 and Sony A380.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Nikon D3100 is 14g lighter than the Sony A380 but we don't think this will make a significant difference.
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 Nikon D3100 and Sony A380 have the same APS-C sized sensor, their lenses for a similar focal length and aperture will be similar in size and weight.
Weather Sealing
Unfortunately neither the Nikon D3100 nor Sony Alpha DSLR-A380 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
Nikon D3100's 3.00" LCD screen is slightly larger than Sony A380's 2.7 screen.