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-H15 and Pentax K20D side-by-side from the front, back and top in their relative dimensions. Casio EX-H15 has external dimensions of 101 x 60 x 28 mm (3.98 x 2.36 x 1.1″) and weighs 161 g (0.35 lb / 5.68 oz) (including batteries). Pentax K20D has external dimensions of 142 x 101 x 70 mm (5.59 x 3.98 x 2.76″) and weighs 800 g (1.76 lb / 28.22 oz) (including batteries).
Below you can see the front-view size comparison of the Casio EX-H15 and the Pentax K20D. Casio EX-H15 is clearly the smaller of the two cameras. Its body is 41mm narrower, 41mm shorter and 42mm thinner than Pentax K20D. As you can tell, actually this is not a fair size comparison since Casio EX-H15 has a built-in lens but Pentax K20D doesn't. Once you put a lens on K20D, its thickness will increase significantly.
Here is the back view size comparison of the Casio EX-H15 and Pentax K20D.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Casio EX-H15 is significantly lighter (639g ) than the Pentax K20D 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 K20D, the total kit will weigh much higher.
Weather Sealing
Thanks to the weather-sealed body of the K20D, you can use this camera with more confidence under conditions where there is risk of exposure to water and dust compared to the EX-H15.
LCD Screen Size and Features
Casio EX-H15's 3.00" LCD screen is slightly larger than Pentax K20D's 2.7 screen.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.