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 Canon SX120 IS and Olympus E-PM1 side-by-side from the front, back and top in their relative dimensions. Canon SX120 IS has external dimensions of 111 x 71 x 45 mm (4.37 x 2.8 x 1.77″) and weighs 285 g (0.63 lb / 10.05 oz) (including batteries). 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).
Below you can see the front-view size comparison of the Canon SX120 IS and the Olympus E-PM1. Olympus E-PM1 is clearly the smaller of the two cameras. Its body is 1mm narrower, 7mm shorter and 11mm thinner than Canon SX120 IS. As you can tell, actually this is not a fair size comparison since Canon SX120 IS has a built-in lens but Olympus E-PM1 doesn't. Once you put a lens on E-PM1, 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.
Olympus E-PM1 is 20g lighter than the Canon SX120 IS but we don't think this will make a significant difference.
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 Canon PowerShot SX120 IS nor Olympus PEN E-PM1 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 Compact Cameras with Weather Sealing Top Mirrorless Cameras with Weather Sealing
LCD Screen Size and Features
Canon SX120 IS and Olympus E-PM1'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.