A delay of 400 milliseconds, about the blink of an eye, causes people to search less, they said.
"Subconsciously, you don't like to wait," Arvind Jain, Google's resident speed guru, told The New York Times. "Every millisecond matters."
Internet users will visit a commercial or news Web site less often if it is slower than a close competitor by more than 250 milliseconds, experts said.
And the quest for speed is becoming more important as data-hungry smartphones and tablets create digital traffic jams as people download maps, videos, news updates and other content, analysts said.
"Two hundred fifty milliseconds, either slower or faster, is close to the magic number now for competitive advantage on the Web," Harry Shum, a computer scientist and speed specialist at Microsoft, said.