Nikon D3100 vs Nikon D5100

This is a full comparison between the cameras Nikon D3100 and Nikon D5100. We compare them by looking at the categories you see below.

Manufacturing

These cameras are both manufactured by Nikon.

Type of camera

Both these cameras are DSLR cameras. No difference there.

Sensors / crop factor

Both these cameras have the same sorts of sensor (called "DX") which means that if you compare these cameras side by side the lenses will also have the same experienced focal length. Neither of the cameras has a Full frame sensor which means that you will get a "crop factor" where the camera's sensor size affect the focal length with a multiplier.

** Experienced focal length when using a lens such as a common "50mm f/1.8"

Learn more about crop factor and focal length multiplier here:
Camera selection can affect the focal length (Nikon)

Resolution

Nikon D3100 has a 14,2 MP (Megapixels) resolution while Nikon D5100 has 16,2 MP. If we break down this in more detail this is the data behind the numbers:

Nikon D5100 has a 14 % larger resolution than Nikon D3100. This could give you more details in the picture but also a possibility to crop more in the pictures, afterward while editing the pictures, if needed that is.

ISO range

Nikon D3100 has a larger ISO-range than Nikon D5100. Nikon D3100 has an ISO range that stretches from 100 to 12800 while Nikon D5100 has 100 to 6400.

Autofocus and lens compatibility

Neither of these two cameras has a built-in autofocus motor. Some lenses, that supports autofocus, do not have an autofocus motor of their own, and often they rely on the cameras providing this autofocus motor but since these two camera models do not have this either it will result in no autofocus is possible.

Here is a complete overview of which lenses work with each camera:
Lens compatibility chart for Nikon D3100
Lens compatibility chart for Nikon D5100

Pictures per second

Depending on what you are shooting the FPS, or frames/pictures per second, can definitely be of interest. Nikon D3100 can shoot up to 3 pictures per seconds and Nikon D5100 can shoot up to 4 pictures per seconds.

Ability to record movies

It is becoming more and more popular to record movies with digital cameras.

In this case, both Nikon D3100 and Nikon D5100 can shoot movies.

Weight

The weight of the camera can be an extremely important factor, especially if the camera is about to be used, or carried around, for several hours at a time.

Nikon D5100 weighs 611 gr (equal to 1,35 lb) which is 21% heavier than Nikon D3100 and its 505 gr (or 1,11 lb).