Collect the necessary information -- the article or amendment number, section and clause referenced.
List the number of the amendment or the number of the article in Roman numerals, but list other numbers using Arabic numerals.
Cite each amendment or article used. Don’t cite the entire U.S. Constitution. Use a footnote for each section of the Constitution you reference so that readers will know exactly where you found the information.
List the footnote as the abbreviated form of the Constitution (U.S. Const.), whether it is an amendment or an article and the section and clause numbers. For example:
[Amendment] U.S. Const. amend. XI. Sec. 2. [Article] U.S. Const. art. 2. sec. 3. cl. 1.