Central Park is 4.7 times larger than Greenwich Park.
Area: 3 km2 calculated
Central Park is an urban park in the New York City borough of Manhattan. It was initially opened in 1857, on 778 acres of city-owned land. In 1858, Frederick Law Olmsted and Calvert Vaux won a design competition to improve and expand the park with a plan they titled the Greensward Plan. Wikipedia
Area: 1 km2 calculated
Greenwich Park is a former hunting park in Greenwich and one of the largest single green spaces in south-east London. One of the Royal Parks of London, and the first to be enclosed, it covers 74 hectares, and is part of the Greenwich World Heritage Site. Wikipedia