Let’s say a salad dressing recipe calls for 2 parts oil and 1 part vinegar. The ratio of those two ingredients is 2 to 1. That means that the amount of oil will be double the amount of vinegar. So if you want enough salad dressing to feed your family, you might choose to make 1-1/2 cups, or 1 cup of oil to 1/2 cup vinegar. If you would like a small amount of dressing, say 3 ounces, you would use 2 tablespoons oil and 1 tablespoon vinegar. Both examples have the same ratio of 2 to 1.