What is the Optimal Virtual Memory Size For 8 GB RAM | WIN 10?

Automatic Method

Windows 10 automatically manages the pagefile for your computer's configuration and the amount of RAM present in it. Typically you'll simply allow the Windows OS to dynamically manage this since in most cases that'll suffice and it'll work just fine.

The minimum and maximum size of the Pagefile can be up to 1.5 times and 4 times of the physical memory that your computer has respectively. For example, if your computer has 1 GB of RAM, the minimum Pagefile size can be 1.5 GB, and the maximum size of the file can be 4 GB.

_Source

Manual Method

To calculate the "general rule" recommended size of virtual memory in Windows 10 per the 8 GB your system has, here's the equation 1024 x 8 x 1.5 = 12288 MB. So it sounds as if the 12 GB configured in your system currently is correct so when or if Windows needs to utilize the virtual memory, the 12 GB should suffice.

As a general rule, the maximum size of the paging file must be x1.5 the amount of RAM installed. Thus for a PC running with 4GB of RAM, the maximum size of the swap file will be 1024 x 4 x 1.5 Mb.

_Source

Fine-Tuned Method (Critical Systems)

It's probably true there is no 'one size fits all' formula for Windows 10 systems that are super fine-tuned to find the most optimal configuration per those systems.

In these cases, depending on various factors of the system and what's important for the system processes, there are many other factors to consider obviously.

There are many options available to record and measure system performance metrics to help benchmark and super fine-tune this configuration if needed though.

While all this is really just a trivial matter, it'll add some complexity and time to get the most optimal configuration where this setting must be the most optimal.

In most cases though using 1.5 times virtual memory for the amount of total RAM on Windows 10 systems will suffice and keep it simple or be a good enough starting point if simply allowing Windows 10 to manage it automatically will not work.