One square of unsweetened or semi-sweet baking chocolate is equal to 1 ounce. If a cook doesn't have chocolate, he or she can make a substitution using cocoa powder and other ingredients.
To make the equivalent of 1 ounce of semi-sweet chocolate, use 3 tablespoons of semi-sweet chocolate chips or combine one square of unsweetened chocolate with 1 tablespoon sugar.
If the recipe calls for 1 ounce of unsweetened chocolate, mix together 3 tablespoons cocoa powder with 1 tablespoon vegetable shortening.
Recipes calling for a 4-ounce bar of sweet baking chocolate can instead include 1/4 cup of cocoa powder with 1/3 cup sugar and 3 tablespoons vegetable shortening.