- American Locomotive Company's Big Boy
- 39.852/508.02 tonne(s)/metric ton(s)
- United States ()
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.