The Section 232 metal weight calculation changed fundamentally on 6 April 2026. For years, duties on steel and aluminum derivative articles were assessed only on the value of the metal inside the product. That apportionment is gone. Duty is now calculated on the full customs value of the article, and metal weight determines whether relief applies and which rate you pay. For importers of record and trade compliance teams, the figure that now drives duty exposure is the metal content expressed as a percentage of total article weight.

This guide explains what changed, how the rates work, and four worked examples by tier, using illustrative figures rather than client data. If you want a structured read on your current exposure, you can request a compliance review at any point.

Key Takeaways

📌 Since 6 April 2026, Section 232 duties on steel, aluminum, copper, and their derivatives apply to the full customs value of the imported article, not only the metal-content value.

📊 The full-value rates are 50% (Annex I-A), 25% (Annex I-B), and a temporary 15% floor (Annex III, through 31 December 2027).

⚠️ A derivative article outside Harmonized Tariff Schedule (HTS) Chapters 72, 73, 74, and 76 is excluded from Section 232 when the covered metal is less than 15% of total article weight. This de minimis relief does not reach those four chapters.

🔗 Metal origin now sets a reduced rate: 10% for U.S.-origin metal and reduced UK rates, each conditioned on melt, pour, smelt, and cast provenance.

📄 The metal-content number is now a weight figure in kilograms that importers must be able to substantiate to U.S. Customs and Border Protection (CBP) with a bill of materials and supplier documentation.

🏭 Automotive, industrial machinery, electronics, aerospace, and construction products importers carry the largest exposure because mixed-material derivatives sit across all three metals.

What changed on 6 April 2026

On 2 April 2026, the President issued Proclamation 11021, “Strengthening Actions Taken to Adjust Imports of Aluminum, Steel, and Copper Into the United States.” Effective for entries on or after 12:01 a.m. eastern daylight time on 6 April 2026, Section 232 additional duties apply to the full customs value of covered aluminum, steel, and copper articles and their derivatives, regardless of metal content, per the White House proclamation and the Federal Register publication (91 FR 18201).

The prior two-line pattern, where importers split out the steel or aluminum content on the commercial invoice and applied the tariff to that portion, no longer applies to covered derivatives. CBP operational guidance in CSMS #68253075 confirms that duties of 10% to 50% now apply to the full customs value from all countries. This shift sits squarely inside trade and customs compliance, and it connects directly to how your team manages HTS classification across the product portfolio.

Section 232 metal weight calculation now applies duty to full customs value

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How is Section 232 duty calculated on a steel part

Two questions set the outcome. First, how is the article classified in the HTS. Second, what is the covered metal content by weight. Classification decides the rate tier and whether de minimis relief is even available. Metal weight decides whether a derivative qualifies for exclusion.

The regime now divides covered products across annexes with distinct rates, all assessed on full customs value.

Two structural rules matter. A product containing more than one covered metal is subject to Section 232 only once, even if it contains steel, aluminum, and copper. The regime has also continued to expand through 2026 via later proclamations and additional derivative listings, so the current HTS annex lists should be confirmed at the time of entry.

The 15% de minimis rule and where it does not apply

The proclamation introduced a de minimis exclusion that is worth real money to the right importer, and it is the point most often misread. A derivative article classified outside HTS Chapters 72, 73, 74, and 76 falls outside Section 232 metals coverage when the aggregate weight of the covered metal is less than 15% of the total weight of the article. The relevant HTS provision is 9903.82.03, carrying a 0% rate.

Three qualifications control the outcome:

✓ The test is measured by weight, not by value. CBP requires the aggregate metal weight in kilograms to be reported at entry.

⚠️ Articles in Chapters 72, 73, 74, and 76 receive no de minimis relief. A mill product or an article made wholly of the metal pays the full-value rate regardless of any weight calculation.

📊 Where an article is flagged for more than one covered metal, use the aggregate weight of all listed metals against total article weight.

This is why country-of-origin determination and part-level weight data now sit on the critical path for duty. The claim is only as strong as the evidence behind it, and CBP can request the bill of materials and product specifications that support it.

Four worked examples by tier

The examples below use a $10,000 customs value and illustrative weights. They are not client figures.

Example 1: an article mostly of metal

A hot-rolled steel bar classified in Chapter 72, foreign-origin steel, $10,000 customs value.

Because it is a Chapter 72 article, it falls in Annex I-A and receives no de minimis relief. Duty is 50% of the full customs value.

Section 232 duty = 50% × $10,000 = $5,000.

Example 2: a derivative above 15% metal

A steel-framed enclosure classified outside Chapters 72 to 76, listed in Annex I-B, $10,000 customs value, steel at 40% of article weight.

The article is outside the four chapters, so de minimis is possible in principle, but the metal is at or above 15% by weight, so the exclusion does not apply. The Annex I-B rate of 25% applies to the full customs value. Under the pre-April metal-content method, duty might have been assessed only on the steel value, an illustrative $3,000, producing a far smaller figure. The full-value basis is the material change.

Section 232 duty = 25% × $10,000 = $2,500.

Example 3: a derivative below 15% metal

An electronic assembly with a small aluminum bracket, classified outside Chapters 72 to 76, $10,000 customs value, aluminum at 8% of article weight.

The article is outside the four chapters and the covered metal is less than 15% of total weight, so it qualifies for the de minimis exclusion under 9903.82.03.

Section 232 duty = $0, provided the importer reports the aggregate metal weight in kilograms and can substantiate it on request.

Example 4: U.S.-melted metal and the 10% rate

A derivative article manufactured abroad from U.S.-origin steel, $10,000 customs value.

A reduced 10% rate applies to derivatives whose covered metal is of U.S. origin, defined as steel melted and poured in the United States, or aluminum and copper smelted and cast in the United States. The qualifying threshold was at least 95% by weight under the April proclamation and was reduced to at least 85% by weight by the June 1, 2026 proclamation (91 FR 34085). Qualifying requires origin evidence such as mill certificates.

Section 232 duty = 10% × $10,000 = $1,000, in place of the 25% or 50% rate that would otherwise apply.

Section 232 metal weight calculation decision flow for steel and aluminum derivatives

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Data to request from suppliers

The duty outcome now depends on data most suppliers have never been asked to certify at this level. For each covered part, request:

1. HTS classification, to confirm whether the article sits in Chapters 72, 73, 74, 76 or in a derivative annex.

2. Covered-metal content by weight in kilograms for steel, aluminum, and copper, aggregated where more than one metal is flagged.

3. Total article weight in kilograms, the denominator for the 15% de minimis test.

4. Country of melt and pour for steel, and smelt and cast for aluminum and copper, with the percentage of U.S.-origin or UK-origin metal by weight.

5. Supporting evidence, including mill test reports, certificates of origin, and the bill of materials that substantiates the metal-content figure.

Mill certificates are central to the 10% U.S.-origin claim, which is why how to read a mill test report is a useful companion reference. Collecting and validating this evidence at scale is a documented pressure point, as covered in the analysis of how tariffs and reshoring are increasing documentation workloads. Routing these requests through structured supplier documentation rather than email reduces the gaps that lead CBP to assess duty on full value when content cannot be proven.

Who is affected and where documentation breaks down

The importers carrying the most exposure are those whose products combine metal with non-metal components across the three covered metals. That includes automotive manufacturing, industrial machinery and heavy equipment, electronics, aerospace, and construction products. Firms that previously relied on metal-content apportionment to limit duty now face full-value assessment unless a part qualifies for de minimis relief or an origin-based rate.

Documentation is the common failure point. The duty is only as defensible as the metal-weight and origin evidence behind it, and that evidence has to be retrievable at the part level, time-stamped, and tied to a specific entry. This is where staying audit-ready across frameworks matters: a CBP request, a customer audit, or a post-entry review all ask the same question, which is whether you can show the content and origin figures you declared. The reshoring pressure this creates is explored further in where Buy American and global supply chains break down, and it connects to parallel domestic-sourcing regimes such as Build America, Buy America.

How Certivo supports Section 232 metal weight calculation

Section 232 is now a part-level data problem. The decisive figures, metal weight as a percentage and metal origin by weight, live in bills of materials and supplier certificates, not in a tariff schedule. Managing that at portfolio scale is where Certivo’s CORA-powered regulatory intelligence applies.

CORA is a deterministic compliance engine, traceable and explainable, that works across 150+ regulations and standards. For this regime it supports a continuous workflow: mapping BOM parts to their HTS classification and the applicable annex, running automated supplier campaigns to collect mill certificates and origin data, applying the 15% weight test and the origin thresholds deterministically, and generating the audit-ready documentation an importer needs to substantiate a de minimis or 10% claim. As later proclamations add derivatives, the engine re-screens affected parts and flags where exposure has changed, which keeps classification and content data current rather than static.

The objective is practical. Reduce duty surprises, shorten evidence retrieval, and give trade compliance a defensible record for every covered entry. To pressure-test your exposure across products and suppliers, request a Section 232 compliance review or speak with a compliance specialist.