Size and weight is a big decision factor when you are trying to find the ideal camera for your needs.
In this section, We are going to illustrate Panasonic G9 and Pentax RZ18 side-by-side from the front, back and top in their relative dimensions. Panasonic G9 has external dimensions of 137 x 97 x 92 mm (5.39 x 3.82 x 3.62″) and weighs 658 g (1.45 lb / 23.21 oz) (including batteries). Pentax RZ18 has external dimensions of 97 x 61 x 33 mm (3.82 x 2.4 x 1.3″) and weighs 178 g (0.39 lb / 6.28 oz) (including batteries).
Below you can see the front view size comparison of Panasonic G9 and Pentax RZ18. Pentax RZ18 is clearly the smaller of the two cameras. Its body is 40mm narrower, 36mm shorter and 59mm thinner than Panasonic G9. As you can tell, actually this is not a fair size comparison since Pentax RZ18 has a built-in lens but Panasonic G9 doesn't. Once you put a lens on G9, its thickness will increase significantly.
Here is the back view size comparison of Panasonic G9 and Pentax RZ18.
Now lets look at the top view comparison of Panasonic G9 and Pentax RZ18.
Weight is another important factor especially when deciding on a camera that you want to carry with you all day.
Pentax RZ18 is significantly lighter (480g ) than the Panasonic G9 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 G9, the total kit will weigh much higher.
Both G9 and RZ18 have weather sealings in their body, making them resistant to water and dust.
LCD Screen Size and Features
Panasonic G9 and Pentax RZ18's LCD screens has the same diagonal size of 3.00".
On the other hand, Panasonic G9 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. Pentax RZ18's LCD screen is a fixed type which provides almost no flexibility in shooting positions compared to G9.