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 Olympus E-PL1s 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). 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 the Olympus E-PM1 and the Olympus E-PL1s. Olympus E-PM1 is clearly the smaller of the two cameras. Its body is 5mm narrower, 8mm shorter and 8mm thinner than Olympus E-PL1s.
Here is the back view size comparison of the Olympus E-PM1 and Olympus E-PL1s.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Olympus E-PM1 is significantly lighter (69g ) than the Olympus E-PL1s which may become a big advantage especially on long walking trips.
Also keep in mind that body weight is not the only deciding factor when comparing two interchangeable camera bodies, you also have to take into account the lenses that you will be using with these bodies. Since both Olympus E-PM1 and Olympus E-PL1s have the same Micro Four Thirds lens mount and Four Thirds sized sensors, lenses will not be a differentiator on total size of the system.
Weather Sealing
Unfortunately neither the Olympus PEN E-PM1 nor Olympus PEN E-PL1s 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
LCD Screen Size and Features
Olympus E-PM1's 3.00" 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.