What should the altimeter be set to when climbing through 18,000'?

When climbing through 18,000 feet, the altimeter should be set to 29.92 inches of mercury (inHg). This standard setting corresponds to the transition altitude in the United States, which is 18,000 feet. Above this altitude, pilots are required to set their altimeters to the standardized pressure of 29.92 inHg to ensure consistent altitude references among different aircraft. This procedure helps maintain safe vertical separation between aircraft flying at different altitudes.

Setting the altimeter to any other value, such as 30.00, 29.50, or 30.10, would not align with the standard pressure setting and could lead to discrepancies in altitude readings, potentially resulting in safety issues during flight. Therefore, adjusting the altimeter to 29.92 is crucial for maintaining accurate altitude awareness and ensuring safe operations in the airspace.