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 D3500 and Nikon D3400 side-by-side from the front, back and top in their relative dimensions. Nikon D3500 has external dimensions of 124 x 97 x 70 mm (4.88 x 3.82 x 2.76″) and weighs 365 g (0.80 lb / 12.87 oz) (including batteries). 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).
Below you can see the front-view size comparison of the Nikon D3500 and the Nikon D3400. Nikon D3500 has the same height with Nikon D3400. On the other hand, with a width of 97mm, it is 1 narrower and also with a thickness of 70mm, it is 6mm thinner than Nikon D3400.
Here is the back view size comparison of the Nikon D3500 and Nikon D3400.
Now lets look at the top view comparison of Nikon D3500 and Nikon D3400.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Nikon D3500 is 30g lighter than the Nikon D3400 but we don't think this will make a significant difference.
Also keep in mind that body weight is not the only deciding factor when comparing two interchangeable camera bodies, you also have to take into account the lenses that you will be using with these bodies. Since both Nikon D3500 and Nikon D3400 have the same Nikon F lens mount and APS-C sized sensors, lenses will not be a differentiator on total size of the system.
Weather Sealing
Unfortunately neither the Nikon D3500 nor Nikon D3400 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
LCD Screen Size and Features
Nikon D3500 and Nikon D3400'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.