I make my “homemade” ranch according to how my grandmother made it. She would use four tablespoons. One packet of ranch seasoning (Hidden Valley brand, I haven’t tested others!) is three tablespoons. Now, I buy the shaker jar of the ranch powder and measure with a tablespoon. If you don’t have this jar, and don’t want to open another packet, three tablespoons is just fine!
Find it online: https://sweetpealifestyle.com/bbq-ranch-dressing/