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 Olympus E-PL1s 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). Olympus E-PL1s has external dimensions of 115 x 72 x 42 mm (4.53 x 2.83 x 1.65″) and weighs 334 g (0.74 lb / 11.78 oz) (including batteries).
Below you can see the front view size comparison of Casio EX-Z450 and Olympus E-PL1s. Casio EX-Z450 is clearly the smaller of the two cameras. Its body is 34mm narrower, 16mm shorter and 21mm thinner than Olympus E-PL1s. As you can tell, actually this is not a fair size comparison since Casio EX-Z450 has a built-in lens but Olympus E-PL1s doesn't. Once you put a lens on E-PL1s, its thickness will increase significantly.
Here is the back view size comparison of Casio EX-Z450 and Olympus E-PL1s.
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 (206g ) than the Olympus E-PL1s 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 E-PL1s, the total kit will weigh much higher.
Unfortunately neither Casio Exilim EX-Z450 nor Olympus PEN E-PL1s 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 Mirrorless Cameras with Weather Sealing
LCD Screen Size and Features
Casio EX-Z450's 3" LCD screen is slightly larger than Olympus E-PL1s's 2.7" screen.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.