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 Nikon D3400 and Ricoh GR III side-by-side from the front, back and top in their relative dimensions. Nikon D3400 has external dimensions of 124 x 98 x 76 mm (4.88 x 3.86 x 2.99″) and weighs 395 g (0.87 lb / 13.93 oz) (including batteries). Ricoh GR III has external dimensions of 109 x 62 x 33 mm (4.29 x 2.44 x 1.3″) and weighs 257 g (0.57 lb / 9.07 oz) (including batteries).
Below you can see the front-view size comparison of the Nikon D3400 and the Ricoh GR III. Ricoh GR III is clearly the smaller of the two cameras. Its body is 15mm narrower, 36mm shorter and 43mm thinner than Nikon D3400. As you can tell, actually this is not a fair size comparison since Ricoh GR III has a built-in lens but Nikon D3400 doesn't. Once you put a lens on D3400, its thickness will increase significantly.
Here is the back view size comparison of the Nikon D3400 and Ricoh GR III.
Now lets look at the top view comparison of Nikon D3400 and Ricoh GR III.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Ricoh GR III is significantly lighter (138g ) than the Nikon D3400 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 D3400, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither the Nikon D3400 nor Ricoh GR III 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 DSLR Cameras with Weather Sealing Top Compact Cameras with Weather Sealing
LCD Screen Size and Features
Nikon D3400 and Ricoh GR III'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.