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 Nikon P300 and Panasonic GF5 side-by-side from the front, back and top in their relative dimensions. Nikon P300 has external dimensions of 103 x 58 x 32 mm (4.06 x 2.28 x 1.26″) and weighs 189 g (0.42 lb / 6.67 oz) (including batteries). Panasonic GF5 has external dimensions of 108 x 67 x 37 mm (4.25 x 2.64 x 1.46″) and weighs 267 g (0.59 lb / 9.42 oz) (including batteries).
Below you can see the front view size comparison of Nikon P300 and Panasonic GF5. Nikon P300 is clearly the smaller of the two cameras. Its body is 5mm narrower, 9mm shorter and 5mm thinner than Panasonic GF5. As you can tell, actually this is not a fair size comparison since Nikon P300 has a built-in lens but Panasonic GF5 doesn't. Once you put a lens on GF5, its thickness will increase significantly.
Now lets look at the top view comparison of Nikon P300 and Panasonic GF5.
Weight is another important factor especially when deciding on a camera that you want to carry with you all day.
Nikon P300 is significantly lighter (78g ) than the Panasonic GF5 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 GF5, the total kit will weigh much higher.
Unfortunately neither Nikon Coolpix P300 nor Panasonic Lumix DMC-GF5 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
Nikon P300 and Panasonic GF5'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.