How much gypsum is required to coagulate one litre/gallon of soy milk From what I could gather from the internet about homemade tofu, information on the subject is divided into two sources:
1. By gypsum manufacturers - they say one tsp of the coagulant is sufficient to 5 gallons.
2. Home made tofu bloggers - 2 tsp per gallon is required to coagulate the milk.

So, how much gypsum is required per gallon?! Confused...
I have The Book of Tofu by William Shurtleff, and the more recent Asian Tofu by Andrea Nguyen. 

Shurtleff recommends 2 tsp of gypsum for 7 1/2 to 8 cups of soy milk.
Nguyen recommends 1 1/2 tsp for 8 cups of soy milk.

(These recipes are for about 1/2 gallon of soy milk. There are 16 cups in a gallon)

I can't verify with personal experience, as I use Epsom salts (magnesium sulfate) as a coagulent, but have had success with both books.  So, I am sure they would both work.