Some people were not happy with this question, as other venues (such as the Indianapolis Motor Speedway) have far bigger capacities. However, Wikipedia does give the Rungrado 1st of May Stadium as the world's largest sports stadium. It also says, "Race tracks (such as the Indianapolis Motor Speedway and the Tokyo Racecourse) are not stadiums, and are not included here."
The question specifically asked about the largest stadium.
On a separate page, Wikipedia lists the world's largest sports venues by capacity. The Indianapolis Motor Speedway does top this list (with a capacity of 257,325); Circuit de la Sarthe (venue of the Le Mans 24 Hours race) is second with 234,800, and Tokyo Racecourse is third with 223,000. The Rungrado 1st of May Stadium is 30th.
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