rogerkf5 writes on nola.com: a roux should be a 1 to 1 ratio but by weight, not by volume. one cup of oil weighs 7.7 ounces, and 1 cup of flour weighs 4.5 ounces. so, a proper ratio would be 1 cup of oil, and 7.7 ounces by weight of flour, close to 1-3/4 cup of all-purpose flour.