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 Casio EX-H20G and Canon 450D side-by-side from the front, back and top in their relative dimensions. Casio EX-H20G has external dimensions of 103 x 68 x 29 mm (4.06 x 2.68 x 1.14″) and weighs 216 g (0.48 lb / 7.62 oz) (including batteries). Canon 450D has external dimensions of 129 x 98 x 62 mm (5.08 x 3.86 x 2.44″) and weighs 524 g (1.16 lb / 18.48 oz) (including batteries).
Below you can see the front-view size comparison of the Casio EX-H20G and the Canon 450D. Casio EX-H20G is clearly the smaller of the two cameras. Its body is 26mm narrower, 30mm shorter and 33mm thinner than Canon 450D. As you can tell, actually this is not a fair size comparison since Casio EX-H20G has a built-in lens but Canon 450D doesn't. Once you put a lens on 450D, its thickness will increase significantly.
Here is the back view size comparison of the Casio EX-H20G and Canon 450D.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Casio EX-H20G is significantly lighter (308g ) than the Canon 450D 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 450D, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither the Casio Exilim EX-H20G nor Canon EOS 450D (EOS Rebel XSi / EOS Kiss X2) 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 DSLR Cameras with Weather Sealing
LCD Screen Size and Features
Casio EX-H20G and Canon 450D's LCD screens have the same diagonal size of 3.00 inches.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.