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 Canon SX120 IS and Pentax Q 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). Pentax Q has external dimensions of 98 x 57 x 31 mm (3.86 x 2.24 x 1.22″) and weighs 180 g (0.40 lb / 6.35 oz) (including batteries).
Below you can see the front view size comparison of Canon SX120 IS and Pentax Q. Pentax Q is clearly the smaller of the two cameras. Its body is 13mm narrower, 14mm shorter and 14mm 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 Pentax Q doesn't. Once you put a lens on Q, 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 Q is significantly lighter (105g ) than the Canon SX120 IS 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 Q, the total kit will weigh much higher.
Unfortunately neither Canon PowerShot SX120 IS nor Pentax Q 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
Canon SX120 IS and Pentax Q's LCD screens has the same diagonal size of 3".
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.