How many days did it take to build the Empire State Building?

The Empire State Building took 410 days to build, from the start of construction to structural completion in April 1931.

Construction began on March 17, 1930, after the former Waldorf–Astoria hotel had been demolished. The project moved at extraordinary speed because design, material fabrication, deliveries, and steel erection were tightly coordinated. Workers sometimes raised an entire floor in a day, and the steel frame reached its top on September 19, 1930.

The 410-day figure refers to structural completion, not the building's public opening. The structure was finished on April 11, 1931—12 days ahead of schedule—and officially opened on May 1. That distinction explains why some accounts describe the project as taking about 13½ months: they are measuring from groundbreaking to opening rather than to completion.

The 102-story skyscraper was designed by Shreve, Lamb & Harmon and built by Starrett Brothers and Eken. More than 3,500 people worked on the project at its peak, including Mohawk ironworkers from the Kahnawake reserve near Montreal. Its speed became one of the building's enduring engineering legends.