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 Pentax K-01 and Nikon P310 side-by-side from the front, back and top in their relative dimensions. Pentax K-01 has external dimensions of 122 x 79 x 58 mm (4.8 x 3.11 x 2.28″) and weighs 561 g (1.24 lb / 19.79 oz) (including batteries). Nikon P310 has external dimensions of 103 x 58 x 32 mm (4.06 x 2.28 x 1.26″) and weighs 194 g (0.43 lb / 6.84 oz) (including batteries).
Below you can see the front-view size comparison of the Pentax K-01 and the Nikon P310. Nikon P310 is clearly the smaller of the two cameras. Its body is 19mm narrower, 21mm shorter and 26mm thinner than Pentax K-01. As you can tell, actually this is not a fair size comparison since Nikon P310 has a built-in lens but Pentax K-01 doesn't. Once you put a lens on K-01, its thickness will increase significantly.
Now lets look at the top view comparison of Pentax K-01 and Nikon P310.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Nikon P310 is significantly lighter (367g ) than the Pentax K-01 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 K-01, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither the Pentax K-01 nor Nikon Coolpix P310 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 Mirrorless Cameras with Weather Sealing Top Compact Cameras with Weather Sealing
LCD Screen Size and Features
Pentax K-01 and Nikon P310's LCD screens have the same diagonal size of 3.00 inches.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.