COMEX vs LME
COMEX, run by CME Group in New York, is the main US metals futures venue; the LME in London leads global base-metal trading.
COMEX trades futures in gold, silver, copper and other metals, and its copper contract is quoted in US cents per pound. The LME (London Metal Exchange) trades base metal contracts, including copper, aluminum and nickel, backed by a warehouse network and daily settlement prices. The two copper prices differ by a spread driven by tariffs, freight and regional inventories.
Traders care because the spread shows where metal is needed. A large COMEX premium can pull copper into US warehouses, and a tariff change can widen or close the gap quickly. Units differ between exchanges, so convert before comparing prices.
Worked example (illustrative numbers, not real data): LME copper at 9,000 dollars per tonne and COMEX copper equivalent to 9,600 dollars per tonne after unit conversion. The 600 dollar premium is the first input to a shipping and duty calculation.