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 P100 and Nikon D3100 side-by-side from the front, back and top in their relative dimensions. Nikon P100 has external dimensions of 114 x 83 x 99 mm (4.49 x 3.27 x 3.9″) and weighs 481 g (1.06 lb / 16.97 oz) (including batteries). 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).
Below you can see the front-view size comparison of the Nikon P100 and the Nikon D3100. Nikon P100 is 10mm narrower and 13mm shorter than Nikon D3100 but it is also 24mm thicker. As you can tell, actually this is not a fair size comparison since Nikon P100 has a built-in lens but Nikon D3100 doesn't. Once you put a lens on D3100, its thickness will increase significantly.
Here is the back view size comparison of the Nikon P100 and Nikon D3100.
Now lets look at the top view comparison of Nikon P100 and Nikon D3100.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Nikon P100 is 24g lighter than the Nikon D3100 but we don't think this will make a significant difference.
Again, this comparison may not be very useful in real life as we are comparing the weight of a camera with a built-in lens to the body-only weight of an interchangeable lens camera. Once you put a lens on D3100, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither the Nikon Coolpix P100 nor Nikon D3100 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 Bridge Cameras with Weather Sealing Top DSLR Cameras with Weather Sealing
LCD Screen Size and Features
Nikon P100 and Nikon D3100's LCD screens have the same diagonal size of 3.00 inches.
On the other hand, Nikon P100 features a
Tilting screen where you can change the angle of the screen to make it easier to shoot from waist or over-the-head levels whereas the Nikon D3100 has a fixed type screen which provides less flexibility in shooting positions compared to P100.