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 GM1 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 GM1 has external dimensions of 99 x 55 x 30 mm (3.88 x 2.16 x 1.2″) and weighs 204 g (0.45 lb / 7.20 oz) (including batteries).
Below you can see the front view size comparison of Nikon P300 and Panasonic GM1. Panasonic GM1 is clearly the smaller of the two cameras. Its body is 4mm narrower, 3mm shorter and 2mm thinner than Nikon P300. As you can tell, actually this is not a fair size comparison since Nikon P300 has a built-in lens but Panasonic GM1 doesn't. Once you put a lens on GM1, its thickness will increase significantly.
Comparison image of Nikon P300 and Panasonic GM1 Size, Weight and External Dimensions - Front View
Here is the back view size comparison of Nikon P300 and Panasonic GM1.
Comparison image of Nikon P300 and Panasonic GM1 Size and Weight - Back View
Now lets look at the top view comparison of Nikon P300 and Panasonic GM1.
Top View Comparison image of Nikon P300 and Panasonic GM1 Size
Weight is another important factor especially when deciding on a camera that you want to carry with you all day.
Nikon P300 is 15g lighter than the Panasonic GM1 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 GM1, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither Nikon Coolpix P300 nor Panasonic Lumix DMC-GM1 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 GM1's LCD screens has the same diagonal size of 3.00".
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.