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 S100 and Panasonic G3 side-by-side from the front, back and top in their relative dimensions. Nikon S100 has external dimensions of 99 x 65 x 18 mm (3.9 x 2.56 x 0.71″) and weighs 175 g (0.39 lb / 6.17 oz) (including batteries). Panasonic G3 has external dimensions of 115 x 84 x 47 mm (4.53 x 3.31 x 1.85″) and weighs 336 g (0.74 lb / 11.85 oz) (including batteries).
Below you can see the front-view size comparison of the Nikon S100 and the Panasonic G3. Nikon S100 is clearly the smaller of the two cameras. Its body is 16mm narrower, 19mm shorter and 29mm thinner than Panasonic G3. As you can tell, actually this is not a fair size comparison since Nikon S100 has a built-in lens but Panasonic G3 doesn't. Once you put a lens on G3, its thickness will increase significantly.
Here is the back view size comparison of the Nikon S100 and Panasonic G3.
Now lets look at the top view comparison of Nikon S100 and Panasonic G3.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Nikon S100 is significantly lighter (161g ) than the Panasonic G3 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 G3, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither the Nikon Coolpix S100 nor Panasonic Lumix DMC-G3 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 Compact Cameras with Weather Sealing Top Mirrorless Cameras with Weather Sealing
LCD Screen Size and Features
Nikon S100's 3.50" LCD screen is slightly larger than Panasonic G3's 3" screen.