how much space should be free on hdd for gaming?

[spyguy]

Lets say on a 1tb hard drive for example. When would the limited space begin to slow performance?

 

[terry4536]

The best answer to your question would be to look a the minimum system requirements for the particular game.

But I can tell you that I had the operating system, programs, and a few games on a 128 GB SSD with room to spare.

I did have another HDD for other data though.

 

[terry4536]

Generally on a hard drive, I try to keep around 20 - 30% free. When I get that full it is time to cleanup the drive.

 

[jdcranke07]

Lets say on a 1tb hard drive for example. When would the limited space begin to slow performance?

90% is when you will notice the slowing of processes. Keeping below this and not staying near it is recommended.
If you have the funds, I highly recommend a SATA SSD or an M.2 SSD for your OS & OS pertinent programs while having an HDD for mass storage, including games. A SATA SSD can speed up performance by about 2.5 to 3 times on average.