Sony a7R III vs Sony a9

This is a full comparison between the cameras Sony a7R III and Sony a9. We compare them by looking at the categories you see below.

Sony a7R III

Sony a9

Manufacturing

These cameras are both manufactured by Sony.

These two camera models were both released 2017.

Camera	Released
Sony a7R III	2017
Sony a9	2017

Type of camera

Both these cameras are Mirrorless cameras. No difference there.

Sensors / crop factor

Both these cameras have the same sorts of sensor (called "Sony Full Frame") which means that if you compare these cameras side by side the lenses will also have the same experienced focal length. Since both cameras have a Full frame sensor there will be no crop factor.

Camera	Focal length, 50mm f/1.8 **
Sony a7R III	50 mm Full-frame sensor No crop factor/focal length multiplier
Sony a9	50 mm Full-frame sensor No crop factor/focal length 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 (Sony)

Resolution

Sony a7R III has a 42 MP (Megapixels) resolution while Sony a9 has 24 MP. If we break down this in more detail this is the data behind the numbers:

Camera	Megapixels
Sony a7R III	42 MP 42177408 pixels 7952 x 5304
Sony a9	24 MP 24000000 pixels 6000 x 4000

Sony a7R III has a 76 % larger resolution than Sony a9. 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

Sony a9 has a larger ISO-range than Sony a7R III. Sony a9 has an ISO range that stretches from 100 to 51200 while Sony a7R III has 100 to 32000.

Camera	ISO Range
Sony a7R III	100-32000
Sony a9	100-51200

Autofocus and lens compatibility

Both of these cameras have a built-in autofocus motor. Some lenses, that support autofocus, do not have an autofocus motor of their own but this won't cause any problems with these two cameras.

Here is a complete overview of which lenses work with each camera:
Lens compatibility chart for Sony a7R III
Lens compatibility chart for Sony a9

Pictures per second

Depending on what you are shooting the FPS, or frames/pictures per second, can definitely be of interest. Sony a7R III can shoot up to 10 pictures per seconds and Sony a9 can shoot up to 20 pictures per seconds.

Camera	FPS (Frames per second)
Sony a7R III	10
Sony a9	20

Ability to record movies

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

In this case, both Sony a7R III and Sony a9 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.

Sony a9 weighs 673 gr (equal to 1.48 lb) which is 2% heavier than Sony a7R III and its 657 gr (or 1.45 lb).

Camera	Weight
Sony a7R III	657 gr 1.45 lb
Sony a9	673 gr 1.48 lb