At what approximate elevation must the rolling boil time be extended beyond the standard one minute?

Answer

Above 6,500 feet (or 2,000 meters)

The generally accepted standard requires extending the boil time to three minutes once a rolling boil is achieved for any location situated above 6,500 feet (or 2,000 meters) due to decreased atmospheric pressure.

At what approximate elevation must the rolling boil time be extended beyond the standard one minute?
temperatureSafetydurationwaterboil