What's the recommended coffee to water ratio for cold brew? I was interested today in making some cold brew. I have a french press so I'd like to use that.

What is your recommended brewing time?
Does this make a concentrate?
What ratio do you use later to dilute that concentrate?
First, make sure to study What do I need to start cold-brewing. But since concentrate is not discussed there, I don't think your question is a duplicate. Your French press concentrate could last a couple days, depending on the consumption.

Assuming you divide the volume of the French press by 5, you would need 1 part of ground coffee (the usual coarse grind you use in the press; extraction is weaker at low temperatures but the time makes up for it even with coarse grind) and 4 parts of fresh room-temperature water, which you gently mix and stir. The coffee should sit for about 12-16 hours at room temperature. Then plunge, and here is the concentrate. To dilute, use another 8 parts of cold water or milk (or better, start with 5-6 parts and taste to determine whether you want it still thinner).

Here's my favourite article that discusses dripping methods as well.