There's only one formulation, but the Soylent team has stated that the total volume consumed per day should be based on individual needs (e.g. a petite 5' individual should be consuming less overall than a muscular 6' individual).

edit to add a source (many more are on the forums):

> Then, a bit before midnight, I got a pair of e-mails from two of the folks at Soylent, one from founder Rob Rhinehart and one from customer service vice president Julio Miles. "We encourage Soylent beta testers to decide how much Soylent they require in a day," he said. Rhinehart had a similar message. They both tell me that I don't have to actually eat the entire bag of Soylent.

From http://arstechnica.com/gadgets/2013/08/ars-does-soylent-day-...