Canon 400D weighs 556 g (1.23 lb / 19.61 oz) and has external dimensions of 127 x 94 x 65 mm (5 x 3.7 x 2.56″). Considering that the average weight of DSLR type cameras is 773g, Canon 400D is a remarkably light camera for its class. With a thickness of 65mm, it has an average thickness for its class.
Here is the front and top view image of Canon 400D with the dimensions:
In order to give you a better idea about the real life size of Canon 400D, we have added an image of how it looks next to a credit card and an AA type battery.
Now let's compare Canon 400D size with the camera that it replaced: Canon 350D. Canon 400D has the same height and width with Canon 350D. On the other hand, with a thickness of 65mm, it is 1mm thicker.
Below you can find the comparison of the weight and thickness of Canon 400D with its main competitors:
Canon 400D 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.