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 Sony A390 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). Sony A390 has external dimensions of 128 x 97 x 86 mm (5.04 x 3.82 x 3.39″) and weighs 549 g (1.21 lb / 19.37 oz) (including batteries).
Below you can see the front view size comparison of Casio EX-Z450 and Sony A390. Casio EX-Z450 is clearly the smaller of the two cameras. Its body is 47mm narrower, 41mm shorter and 65mm thinner than Sony A390. As you can tell, actually this is not a fair size comparison since Casio EX-Z450 has a built-in lens but Sony A390 doesn't. Once you put a lens on A390, its thickness will increase significantly.
Here is the back view size comparison of Casio EX-Z450 and Sony A390.
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 (421g ) than the Sony A390 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 A390, the total kit will weigh much higher.
Unfortunately neither Casio Exilim EX-Z450 nor Sony Alpha DSLR-A390 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 Sony A390's 2.7" screen.
On the other hand, Sony A390 LCD screen has a Tilting feature
where you can change the angle of the screen to make it easier to shoot from waist or over the head levels. On the other hand, Casio EX-Z450 has a fixed type screen which provides less flexibility in shooting positions compared to A390.