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 S640 and Nikon S4000 side-by-side from the front, back and top in their relative dimensions. Nikon S640 has external dimensions of 91 x 55 x 21 mm (3.58 x 2.17 x 0.83″) and weighs 130 g (0.29 lb / 4.59 oz) (including batteries). Nikon S4000 has external dimensions of 95 x 57 x 20 mm (3.74 x 2.24 x 0.79″) and weighs 131 g (0.29 lb / 4.62 oz) (including batteries).
Below you can see the front-view size comparison of the Nikon S640 and the Nikon S4000. Nikon S640 is 4mm narrower and 2mm shorter than Nikon S4000 but it is also 1mm thicker.
Here is the back view size comparison of the Nikon S640 and Nikon S4000.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Nikon S640 is 1g lighter than the Nikon S4000 but we don't think this will make a significant difference.
Weather Sealing
Unfortunately neither the Nikon Coolpix S640 nor Nikon Coolpix S4000 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
LCD Screen Size and Features
Nikon S4000's 3.00" LCD screen is slightly larger than Nikon S640's 2.7" screen.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.