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 ELPH 150 IS and Sony A55 side-by-side from the front, back and top in their relative dimensions. Canon ELPH 150 IS has external dimensions of 95 x 57 x 24 mm (3.74 x 2.24 x 0.94″) and weighs 142 g (0.31 lb / 5.01 oz) (including batteries). Sony A55 has external dimensions of 124 x 92 x 85 mm (4.88 x 3.62 x 3.35″) and weighs 500 g (1.10 lb / 17.64 oz) (including batteries).
Below you can see the front-view size comparison of the Canon ELPH 150 IS and the Sony A55. Canon ELPH 150 IS is clearly the smaller of the two cameras. Its body is 29mm narrower, 35mm shorter and 61mm thinner than Sony A55. As you can tell, actually this is not a fair size comparison since Canon ELPH 150 IS has a built-in lens but Sony A55 doesn't. Once you put a lens on A55, its thickness will increase significantly.
Here is the back view size comparison of the Canon ELPH 150 IS and Sony A55.
Now lets look at the top view comparison of Canon ELPH 150 IS and Sony A55.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Canon ELPH 150 IS is significantly lighter (358g ) than the Sony A55 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 A55, the total kit will weigh much higher.
Unfortunately neither the Canon PowerShot ELPH 150 IS (IXUS 155) nor Sony SLT-A55 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 DSLR Cameras with Weather Sealing
LCD Screen Size and Features
Sony A55's 3.00" LCD screen is slightly larger than Canon ELPH 150 IS's 2.7" screen.
Moreover, Sony A55 sports a Fully Articulated screen
which you can change the angle and position of the screen almost freely, making it possible to shoot from waist or over-the-head levels, and especially very useful for shooting selfies and video. On the other hand, Canon ELPH 150 IS has a fixed type screen which provides almost no flexibility in shooting positions compared to A55.