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 Panasonic ZS3 and Sony A500 side-by-side from the front, back and top in their relative dimensions. Panasonic ZS3 has external dimensions of 103 x 60 x 33 mm (4.06 x 2.36 x 1.3″) and weighs 229 g (0.50 lb / 8.08 oz) (including batteries). Sony A500 has external dimensions of 137 x 104 x 84 mm (5.39 x 4.09 x 3.31″) and weighs 630 g (1.39 lb / 22.22 oz) (including batteries).
Below you can see the front view size comparison of Panasonic ZS3 and Sony A500. Panasonic ZS3 is clearly the smaller of the two cameras. Its body is 34mm narrower, 44mm shorter and 51mm thinner than Sony A500. As you can tell, actually this is not a fair size comparison since Panasonic ZS3 has a built-in lens but Sony A500 doesn't. Once you put a lens on A500, its thickness will increase significantly.
Here is the back view size comparison of Panasonic ZS3 and Sony A500.
Now lets look at the top view comparison of Panasonic ZS3 and Sony A500.
Weight is another important factor especially when deciding on a camera that you want to carry with you all day.
Panasonic ZS3 is significantly lighter (401g ) than the Sony A500 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 A500, the total kit will weigh much higher.
Unfortunately neither Panasonic Lumix DMC-ZS3 (Lumix DMC-TZ7) nor Sony Alpha DSLR-A500 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 DSLR Cameras with Weather Sealing
LCD Screen Size and Features
Panasonic ZS3 and Sony A500's LCD screens has the same diagonal size of 3".
On the other hand, Sony A500 features a Tilting screen
where you can change the angle of the screen to make it easier to shoot from waist or over the head levels whereas the Panasonic ZS3 has a fixed type screen which provides less flexibility in shooting positions compared to A500.