Largest steam locomotive

It is generally agreed that the largest steam locomotives are the 4-8-8-4 'Big Boys', built by the American Locomotive Company in 1941-44. They are 39.852 m (130.74 ft) long and weigh 508.02 tonnes (1.12 million lb) with tenders. Twenty-five Big Boys were commissioned by the Union Pacific Railroad for hauling heavy freights up the Sherman Hill section. On test they developed an indicated 7000 hp, with a tractive effort of 61,405 kg (135,375lb) (Tractive effort is the force exerted at the rim of the driving wheel, measured in terms of the weight this force could lift vertically). The Big Boys stand 4.91m (16.1ft) high, are 3.35m (11ft) wide, with a grate area of 13.96m² (150.26ft²), 534.6m² (5754.3ft²) of heating surface plus 189.9m² (2044ft²) of superheater. The four cylinders measure 603 x 813mm (23.7 x 32in). Seven Big Boys survive today.