Van Gaal admitted he was stunned at the size of Manchester United after they beat Real Madrid in front of more than 109,000 fans in America on Saturday night.
Van Gaal said: "We have played on front of 300,000 fans on this tour and now there will be more for the final in Miami (v Liverpool on Monday)
"It is amazing and the impact of the tournament is far greater than anything I experienced in pre-season in Germany or Holland."
Van Gaal could win a first trophy at United in just his third week and said: "You can not read too much into preparation games but Of course it is a very god result and gives confidence.
"I changed a lot of players in the second half and in spite of that we scored again."