It depends on what you mean by equivalent? An ounce is an ounce is an ounce, regardless of what it is an ounce of iyswim. If you mean in terms of nutrition, then it depends what you are measuring. For instance for calcium, 8oz of milk has appx 300 mg of calcium, and yogurt about the same, but you only need about 1.5 ounces of cheese to get the 300 mg of calcium. But if you are looking at fat, protein, calories, etc then it will depend on the fat content, etc etc.