Sony A100 weighs 638 g (1.41 lb / 22.50 oz) and has external dimensions of 133 x 95 x 71 mm (5.24 x 3.74 x 2.8″). Considering that the average weight of DSLR type cameras is 774g, Sony A100 is a remarkably light camera for its class. With a thickness of 71mm, it has an average thickness for its class.
In order to give you a better idea about the real life size of Sony A100, we have added an image of how it looks next to a credit card and an AA type battery.
Now lets compare the weight and thickness of Sony A100 with its main competitors:
Sony A100 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.