(Reuters) -The U.S. tariff rate on most imported steel and aluminum doubled on Wednesday as President Donald Trump ratcheted up a global trade war.

Here's a summary of the major trade partners it will affect.

STEEL:

Roughly a quarter of all steel used in the U.S. is imported, the bulk of it from neighbours Mexico and Canada or close allies in Asia and Europe such as Japan, South Korea and Germany.

While China is the world's largest steel producer and exporter, it sends very little to the United States. Tariffs of 25% imposed in 2018 shut most Chinese steel out of the market.

China exported 508,000 net tons of steel to the U.S. last year or 1.8% of total American steel imports.

ALUMINUM:

For aluminum, the U.S. is more heavily reliant on imports. Roughly half of all aluminum used in the U.S. is imported, with the vast majority coming from Canada. At 3.2 million tons last year, Canadian imports were twice those of the next nine countries combined.

The next largest sources of imports are the United Arab Emirates and China, at 347,034 and 222,872 metric tons, respectively.

The U.S. aluminum smelting industry is small by global standards. Total smelter capacity in the country was just 1.73% of the global total according to the U.S. Geological Survey.

(Reporting by Amy Lv and Lewis Jackson in Beijing, Neha Arora in New Delhi, Francesco Guarascio in Hanoi, Hyunjoo Jin in Seoul; Editing by Michael Perry, Clarence Fernandez and Lincoln Feast.)