On 6 April 2026, the basis for Section 232 duty changed at its foundation. Duties on steel, aluminum, and copper derivatives now apply to the full customs value of the article, not the value of the metal inside it, and metal weight as a percentage of total article weight decides whether relief applies and which rate you pay. For importers of record and trade compliance teams, that shift turns a once-minor invoice line into a measurable source of duty exposure, penalty risk, and audit pressure. The 15% de minimis rule, the origin-based 10% rate, and the requirement to substantiate metal weight in kilograms to CBP all now depend on part-level data most suppliers have never been asked to certify. This analysis of the Section 232 metal weight calculation walks through the rate tiers, the de minimis test, and four worked examples by tier, so trade teams can locate exactly where exposure sits. It also shows why duty defensibility is now a documentation problem: the figure you declare
