The United States is estimated to hold roughly 1.6 million tonnes of copper on and off exchange, according to Macquarie, as the tariff-driven trade that pulled metal into American warehouses begins to lose momentum. ScrapMonster reported on October 15, 2026, that more than 714,000 tonnes sit in COMEX-approved warehouses and that COMEX now holds roughly 70% of the copper visible across the world's major exchanges. The price incentive that drew the metal into the country has narrowed sharply, raising the question of whether copper will keep arriving or eventually start leaving.
The buildup followed President Donald Trump's Section 232 investigation into U.S. copper imports, launched in February 2025. Traders anticipated that imported refined copper could eventually face tariffs, which pushed COMEX prices above comparable London Metal Exchange prices. When the U.S. premium was large enough to cover freight, insurance and other costs, traders could buy copper elsewhere, ship it to the United States and deliver it into COMEX warehouses at a profit.
Since the end of February 2025, COMEX stocks have risen by nearly 750%, according to the report. The scale of the stockpile becomes clearer when compared with normal flows. The U.S.
Geological Survey estimates that American mines produced approximately 1.0 million tonnes of recoverable copper in 2025, which means Macquarie's estimated stockpile is roughly 1.6 times the country's annual mine output. Reuters reports that the United States imported more than 1.62 million tonnes of copper in 2025, an 80% increase from 2024. The figures come from different reporting systems and timing, and ScrapMonster cautions that they should not be treated as a precise inventory reconciliation.
The publication had previously reported a U.S. stockpile estimate of approximately 1.1 million tonnes based on Citi analysis. The newer 1.6-million-tonne figure from Macquarie uses a broader estimate of on- and off-exchange stocks, and the difference should not be read as a 500,000-tonne increase within a matter of days. Still, the roughly 714,000 tonnes on COMEX plus almost 130,000 tonnes registered in U.S.
LME warehouses account for about 844,000 tonnes of the broader estimate, which suggests that a substantial amount of American copper is held outside those two visible exchange systems. The economics of the trade have weakened considerably. The COMEX premium over LME copper reached more than $3,000 per tonne at its peak in July 2025, according to the report.
The spread is now around $310 per tonne, a reduction of almost 90% from the peak. The report notes that the spread can still support certain trades depending on freight, financing and warehouse costs, but the incentive to continuously pull additional copper into the United States has weakened substantially. Most of the copper now stored in the United States is owned by commercial market participants rather than the U.S. government.
That means the metal could theoretically leave the country again. If copper becomes sufficiently scarce in Europe or Asia, LME or Shanghai prices could rise enough relative to COMEX to reverse the trade, giving exporters an economic reason to move U.S. stocks back into international markets. Refined copper remains the key unresolved tariff question.
According to the report, the Commerce Department previously recommended a universal tariff of 15% on refined copper beginning January 1, 2027, and 30% beginning January 1, 2028. The July 2025 presidential proclamation directed Commerce to provide an updated assessment of U.S. copper markets by June 30, 2026, so the President could determine whether those additional duties were warranted. No decision implementing the proposed refined-copper tariff has been publicly announced, so January 1 is a proposed start date rather than an automatic deadline.
Macquarie analyst Alice Fox sees one plausible scenario in which January arrives without a final tariff decision. In that case, the arbitrage could weaken further before recovering to a level high enough to discourage copper from leaving the United States, but not high enough to attract the extraordinary inflows seen previously. The result could be a market in which the United States remains oversupplied while the metal does not immediately flow back to regions where physical copper is tighter.
Although the broader arbitrage is weakening, copper has continued to arrive at some U.S. warehouse locations. LME warehouses in New Orleans and Baltimore held nearly 130,000 tonnes of registered copper, an increase of approximately 44% since mid-August. The report also points to an apparent contradiction in the market.
Macquarie forecasts a global refined-copper surplus of approximately 223,000 tonnes in 2026, with larger surpluses possible from 2027 as mine supply increases. Yet copper prices have recently traded close to record levels. According to the analysis, the explanation lies in geography: a market can have enough copper globally while still experiencing regional shortages if much of that metal is held where other consumers cannot readily access it.
The tariff story also intersects with U.S. copper scrap policy. Copper scrap was excluded from the original Section 232 copper import tariffs. However, the 2025 copper proclamation directed the Commerce Department to implement a domestic-sales requirement covering 25% of high-quality copper scrap produced in the United States.
The policy is intended to improve access to secondary feedstock for U.S. fabricators and refiners. ScrapMonster notes that the exact commercial impact on individual scrap grades will depend on implementation rules, domestic refining demand, export economics and regional buying competition. The timing places the issue in focus ahead of LME Week, which runs October 19 to 23, 2026, in London, with the London Metal Exchange's flagship Metals Seminar scheduled for Monday, October 19.
U.S. refined-copper tariffs, warehouse inventories, global surpluses and the possibility of reversing trade flows are expected to be major discussion points as producers, traders, consumers and investors assess the 2027 outlook. In ScrapMonster's assessment, the central question is shifting. For more than a year, the issue was how much copper the prospect of U.S. tariffs could draw into American warehouses.
With U.S. stocks now estimated at around 1.6 million tonnes and the COMEX-LME arbitrage down almost 90% from its peak, the more important question is what keeps those tonnes in the United States. As long as U.S. prices retain enough premium, the inventory may remain largely in place. If physical shortages outside the United States eventually push London or Shanghai prices decisively above COMEX, the same arbitrage mechanism that built the stockpile could begin working in reverse.
Sources: Reuters; Macquarie (analyst Alice Fox); U.S. Geological Survey; White House; London Metal Exchange; Citi (earlier estimate cited by ScrapMonster); ScrapMonster (reporter Paul Ploumis).
Source: scrapmonster.com