Gone are the days when online shoppers would wait for 2 seconds for your website to load, now they will switch at the blink of an eye.

For Impatient Web Users, an Eye Blink Is Just Too Long to Wait

People will visit a Web site less often if it is slower than a close competitor by more than 250 milliseconds (a millisecond is a thousandth of a second).

“Two hundred fifty milliseconds, either slower or faster, is close to the magic number now for competitive advantage on the Web,” said Harry Shum, a computer scientist and speed specialist at Microsoft.

The performance of Web sites varies, and so do user expectations. A person will be more patient waiting for a video clip to load than for a search result. And Web sites constantly face trade-offs between visual richness and snappy response times. As entertainment and news sites, like The New York Times Web site, offer more video clips and interactive graphics, that can slow things down.

But speed matters in every context, research shows. Four out of five online users will click away if a video stalls while loading.