As per International Monetary Fund (IMF) 2019 estimates, the GDP (nominal) of United States is USD 21,439,453 million. This GDP (nominal) is around 24.57% of Entire World’s GDP. Currently (2019), the world rank of United States is 1 in terms of GDP Nominal.
However, as per 2018 estimates by World Bank, the GDP (Nominal) of United States is USD 20,494,100 million. As per World Bank Estimates, the global rank of United States is 1.

United States GDP [PPP]

On the other hand, as per 2019 estimates by International Monetary Fund, the GDP (PPP) of United States is USD 21,439,453 Million. This is 15.11% of World. United States on this basis has a global rank of 2.