What is the optimal amount of RAM for Photoshop?

I have 40GB of  Ram.  I set Photoshop preferences so that it can use up to 32GB.    When I use Photoshop I rarely see Photoshop use more than 10GB of Ram.  However, I have run some batch script where  Photoshop used all 32GB and also used 120GB of scratch space.   So I would think  for an average user that does not create huge layer documents with hundreds of layers that 16GB would do but the prices of ECC ram is not so great I get 32GB.   My Dell workstation had  8GB before it arrived I had and additional 32GB of ECC Ram from a lower cost supplier waiting to be installed. Its 7 year old now all I had to replace so far was the display adapter. Its quadro 4000 failed for $150 I replaced it with a refurbished Quadro K2200 which is an upgrade  from the 4000.  Your System should boot from SSD and your applications and Photoshop scratch space on SSD

When you load images into Photoshop, they load into RAM memory to work faster. The amount of RAM you need will depend on how many images you want to work on at the same time and how big they're going to be.

You can see how much memory are your images using when opened in the bottom left corner of the application frame.

You would definitely need more ram when creating panoramas as you will be loading lots of images but not as much ram when you only work on one or two images at the same time so 8GB of RAM will be OK for most tasks.

Hi

16GB would be good but 32GB would be even better, depends on how resource hungry your projects are really

https://www.pugetsystems.com/recommended/Recommended-Systems-for-Adobe-Photoshop-139/Hardware-Recommendations