Hyde Park, London is 2.8% larger than Grant Park (Chicago).
Area: 1 km2 calculated
Grant Park is a large urban park in the Loop community area of Chicago. Located in Chicago's central business district, the park's most notable features are Millennium Park, Buckingham Fountain, the Art Institute of Chicago and the Museum Campus. Wikipedia
Area: 1 km2 calculated
Hyde Park is one of the largest parks in London, and one of the Royal Parks of London, famous for its Speakers' Corner. The park was the site of the Great Exhibition of 1851, for which the Crystal Palace was designed by Joseph Paxton. Wikipedia