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 Pentax W80 and Pentax K20D side-by-side from the front, back and top in their relative dimensions. Pentax W80 has external dimensions of 100 x 56 x 25 mm (3.94 x 2.2 x 0.98″) and weighs 156 g (0.34 lb / 5.50 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 Pentax W80 and the Pentax K20D. Pentax W80 is clearly the smaller of the two cameras. Its body is 42mm narrower, 45mm shorter and 45mm thinner than Pentax K20D. As you can tell, actually this is not a fair size comparison since Pentax W80 has a built-in lens but Pentax K20D doesn't. Once you put a lens on K20D, its thickness will increase significantly.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Pentax W80 is significantly lighter (644g ) 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
Both the W80 and the K20D have weather sealings in their bodies, making them resistant to water and dust.
LCD Screen Size and Features
Pentax K20D's 2.70" LCD screen is slightly larger than Pentax W80's 2.5" screen.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.