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 Canon SX20 IS and Nikon D3100 side-by-side from the front, back and top in their relative dimensions. Canon SX20 IS has external dimensions of 128 x 88 x 87 mm (5.04 x 3.46 x 3.43″) and weighs 600 g (1.32 lb / 21.16 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 Canon SX20 IS and the Nikon D3100. Nikon D3100 is 4mm narrower and 12mm thinner than Canon SX20 IS but it is also 8mm taller. As you can tell, actually this is not a fair size comparison since Canon SX20 IS has a built-in lens but Nikon D3100 doesn't. Once you put a lens on D3100, its thickness will increase significantly.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Nikon D3100 is significantly lighter (95g ) than the Canon SX20 IS which may become a big advantage especially on long walking trips.
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 Canon PowerShot SX20 IS 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 D3100's 3.00" LCD screen is slightly larger than Canon SX20 IS's 2.5" screen.
On the other hand, Canon SX20 IS sports a
Fully Articulated screen which you can change the angle and position of the screen almost freely, making it possible to shoot from waist or over-the-head levels, and especially very useful for shooting selfies and video. On the other hand, Nikon D3100 has a fixed type screen which provides almost no flexibility in shooting positions compared to SX20 IS.