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 Olympus E-PM1 and Panasonic ZS8 side-by-side from the front, back and top in their relative dimensions. Olympus E-PM1 has external dimensions of 110 x 64 x 34 mm (4.33 x 2.52 x 1.34″) and weighs 265 g (0.58 lb / 9.35 oz) (including batteries). Panasonic ZS8 has external dimensions of 105 x 58 x 33 mm (4.13 x 2.28 x 1.3″) and weighs 210 g (0.46 lb / 7.41 oz) (including batteries).
Below you can see the front-view size comparison of the Olympus E-PM1 and the Panasonic ZS8. Panasonic ZS8 is clearly the smaller of the two cameras. Its body is 5mm narrower, 6mm shorter and 1mm thinner than Olympus E-PM1. As you can tell, actually this is not a fair size comparison since Panasonic ZS8 has a built-in lens but Olympus E-PM1 doesn't. Once you put a lens on E-PM1, its thickness will increase significantly.
Here is the back view size comparison of the Olympus E-PM1 and Panasonic ZS8.
Now lets look at the top view comparison of Olympus E-PM1 and Panasonic ZS8.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Panasonic ZS8 is significantly lighter (55g ) than the Olympus E-PM1 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-PM1, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither the Olympus PEN E-PM1 nor Panasonic Lumix DMC-ZS8 (Lumix DMC-TZ18) 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 Mirrorless Cameras with Weather Sealing Top Compact Cameras with Weather Sealing
LCD Screen Size and Features
Olympus E-PM1 and Panasonic ZS8'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.