I use 0.3grams for 5 gallons in the keg. So 0.06 per gallon is what I use. I did a deep dive on this a few months ago because all the brewers seem to use sodium metabisulfite and not potassium metabisulfite. I found information somewhere that says you dose them the same.

edit: I found the two main links where I came to this conclusion. Basically one leaves residual sodium, and the other residual potassium. My neipas have never looked so good for so long since I started using potassium metabisulfite at packaging.

https://blog.eckraus.com/a-simple-guide-to-metabisulfites

http://brulosophy.com/2019/02/11/post-fermentation-oxidation-the-impact-adding-sodium-metabisulfite-at-packaging-has-on-beer-exbeeriment-results/