Nikon D3100 weighs 505 g (1.11 lb / 17.81 oz)
and has external dimensions of 124 x 96 x 75 mm (4.88 x 3.78 x 2.95″)
. Considering that the average weight of DSLR type cameras is 773g, Nikon D3100 is a remarkably light camera for its class. With a thickness of 75mm, it has an average thickness for its class.
Here is the front and top view image of Nikon D3100 with the dimensions:
In order to give you a better idea about the real life size of Nikon D3100, we have added an image of how it looks next to a credit card and an AA type battery.
Now let's compare Nikon D3100 size with the camera that it replaced: Nikon D3000. Nikon D3100 is 2mm narrower and 1mm shorter than Nikon D3000 but it is also 11mm thicker.
Below you can find the comparison of the weight and thickness of Nikon D3100 with its main competitors:
Nikon D3100 Size Compared to Main Competitors
Nikon D3100 doesn't have any environmental sealings on its body so you got to be extra careful to protect it against water and dust. If you shoot under these conditions very often, consider checking Top DSLR Cameras with Weather Sealing page.