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.
Weight Comparison
DSLR Cameras
Thickness Comparison
DSLR Cameras
Here is the front and top view image of Nikon D3100 with the dimensions:
Front and Top View External Dimensions and Size of Nikon D3100 Camera Body
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.
Physical size of the Nikon D3100 Body Compared to a Credit Card and an AA 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.
Comparison image of Nikon D3100 and Nikon D3000 Size, Weight and External Dimensions - Front View
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
Weather Sealing
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.