Safety experts have agreed that 50,000 people will be able to attend each day of the Royal Ascot meeting in York in 2005. The famous race meeting is being moved north while building work is carried out at the Berkshire course.
Temporary stands and hospitality areas will enable York's present maximum capacity of around 45,000 to be raised.
There will also be new covered areas to provide shelter from any rain.
Douglas Erskine-Crum, the chief executive of Ascot, said: "We're delighted that the important question of capacity for Royal Ascot at York has been agreed by the City of York Council.
"A joint Ascot and York team proposed the figure of 50,000 based on considerable research into the current and temporary facilities available."