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 D5100 and Canon SX40 HS side-by-side from the front, back and top in their relative dimensions. Nikon D5100 has external dimensions of 128 x 97 x 79 mm (5.04 x 3.82 x 3.11″) and weighs 560 g (1.23 lb / 19.75 oz) (including batteries). Canon SX40 HS has external dimensions of 123 x 92 x 108 mm (4.84 x 3.62 x 4.25″) and weighs 600 g (1.32 lb / 21.16 oz) (including batteries).
Below you can see the front-view size comparison of the Nikon D5100 and the Canon SX40 HS. Canon SX40 HS is 5mm narrower and 5mm shorter than Nikon D5100 but it is also 29mm thicker. As you can tell, actually this is not a fair size comparison since Canon SX40 HS has a built-in lens but Nikon D5100 doesn't. Once you put a lens on D5100, its thickness will increase significantly.
Here is the back view size comparison of the Nikon D5100 and Canon SX40 HS.
Now lets look at the top view comparison of Nikon D5100 and Canon SX40 HS.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Nikon D5100 is 40g lighter than the Canon SX40 HS 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 D5100, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither the Nikon D5100 nor Canon PowerShot SX40 HS 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 Top Bridge Cameras with Weather Sealing
LCD Screen Size and Features
Nikon D5100's 3.00" LCD screen is slightly larger than Canon SX40 HS's 2.7 screen.