To find the GDP of a country, one adds up all consumer spending (C), all investment (I), all government spending minus taxes (G), and the value of exports minus imports ("X – M"). This is shown by the equation:formula_1 This measure is often used to find out how healthy a country is; a country with a high value of GDP can be called a large economy. The United States has the largest GDP in the world. Germany has the largest in Europe, Nigeria in Africa and China in Asia.