What is butter?
In the US, butter must contain at least 80% milk fat by weight (21 U.S.C. § 321a); most of the rest is water, with a little milk solid. That mix is what makes it so useful in baking. Solid and cold, it laminates pastry into flaky layers; soft and creamed with sugar, it traps air for tender cakes; melted, it enriches cookies and quick breads.
A 240 ml reference cup of butter weighs about 227 grams — about two standard US sticks. This calculator uses 15 ml tablespoons and 5 ml teaspoons; the reference cup holds 16 of these tablespoons. Check the spoon standard on packaging before using wrapper marks. For laminated doughs, weighing is the most precise option.