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 A100 and Nikon D3400 side-by-side from the front, back and top in their relative dimensions. Nikon A100 has external dimensions of 95 x 59 x 20 mm (3.74 x 2.32 x 0.79″) and weighs 119 g (0.26 lb / 4.20 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 A100 and the Nikon D3400. Nikon A100 is clearly the smaller of the two cameras. Its body is 29mm narrower, 39mm shorter and 56mm thinner than Nikon D3400. As you can tell, actually this is not a fair size comparison since Nikon A100 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 A100 and Nikon D3400.
Now lets look at the top view comparison of Nikon A100 and Nikon D3400.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Nikon A100 is significantly lighter (276g ) 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 Coolpix A100 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 Compact Cameras with Weather Sealing Top DSLR Cameras with Weather Sealing
LCD Screen Size and Features
Nikon D3400's 3.00" LCD screen is slightly larger than Nikon A100's 2.7 screen.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.