Approximately 2,500 kilograms of gunpowder were used in the Gunpowder Plot.
The conspirators accumulated the explosive beneath the House of Lords in preparation for the State Opening of Parliament on 5 November 1605. Contemporary accounts describe 36 barrels in the cellar, though the gunpowder had deteriorated by the time it was discovered. Even in that condition, the stockpile represented a potentially devastating explosion.
The plotters planned to kill King James I, members of both Houses of Parliament and other leading figures gathered for the ceremony. Guy Fawkes, who had military experience and knowledge of explosives, was left to ignite the powder and escape across the Thames. The intended blast was not merely an attack on one person; it was meant to destroy the political leadership of England.
The often-quoted figure of about 2,500 kilograms is an approximate modern conversion rather than a precisely measured surviving quantity. That is why estimates may vary in summaries. The gunpowder was ultimately removed to the Tower of London, where it was described as decayed. The failed explosion later gave 5 November its enduring Bonfire Night associations.