For 1 cup (8 oz / 225 g) of butter, you can use: 1 cup of margarine; or. 7/8 cup (7 oz / 200 g) lard (or shortening) and 1/2 tsp. salt. 7/8 cup (7 oz / 200 ml) of vegetable oil. Don't substitute oil for butter for in a pastry recipe. It is okay to do so in most recipes for cakes and muffins.