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 Casio EX-Z450 and Pentax K-x side-by-side from the front, back and top in their relative dimensions. Casio EX-Z450 has external dimensions of 81 x 56 x 21 mm (3.19 x 2.2 x 0.83″) and weighs 128 g (0.28 lb / 4.52 oz) (including batteries). Pentax K-x has external dimensions of 123 x 92 x 68 mm (4.84 x 3.62 x 2.68″) and weighs 580 g (1.28 lb / 20.46 oz) (including batteries).
Below you can see the front view size comparison of Casio EX-Z450 and Pentax K-x. Casio EX-Z450 is clearly the smaller of the two cameras. Its body is 42mm narrower, 36mm shorter and 47mm thinner than Pentax K-x. As you can tell, actually this is not a fair size comparison since Casio EX-Z450 has a built-in lens but Pentax K-x doesn't. Once you put a lens on K-x, its thickness will increase significantly.
Here is the back view size comparison of Casio EX-Z450 and Pentax K-x.
Weight is another important factor especially when deciding on a camera that you want to carry with you all day.
Casio EX-Z450 is significantly lighter (452g ) than the Pentax K-x 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 K-x, the total kit will weigh much higher.
Unfortunately neither Casio Exilim EX-Z450 nor Pentax K-x provides any type of weather sealing in their body, 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 DSLR Cameras with Weather Sealing
LCD Screen Size and Features
Casio EX-Z450's 3" LCD screen is slightly larger than Pentax K-x's 2.7 screen.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.