All citations of the U.S. Constitution begin with U.S. Const., followed by the article, amendment, section, and/or clause numbers as relevant. The terms article, amendment, section, and clause are always abbreviated art., amend., §, and cl., respectively. Preamble is abbreviated pmbl. Article and amendment numbers are given in Roman numerals (I, II, III); section and clause numbers are given in Arabic numerals (1, 2, 3).
Example: U.S. Const. art. I, § 3.
Cited in text: (U.S. Const. art. I, § 3.)
Example: U.S. Const. amend. XIX
Cited in text: (U.S. Const. amend. XIX)