Recipe mentions jar of artichokes. What size is the jar?

I usually buy 12 ounce jars of marinated artichoke hearts (because I love them), and I like Nancy's suggestion of starting with about half the jar, and adding more to your taste.

Did you read through the comments? Maybe someone else faced and solved this problem.
Short of that, I'd start with one of the small jars - about 4-5 oz.
Maybe buy two.
Make the dip, taste, and if you want more artichoke flavor or texture, add the contents of the second jar.