At 18,000 feet, approximately how much lower is the pressure compared to sea level?

At 18,000 feet, the atmospheric pressure is indeed significantly lower than at sea level, generally around 50% of the sea level pressure. At sea level, the standard atmospheric pressure is approximately 1013 hPa (hectopascals), whereas at 18,000 feet, the pressure drops to about 500 hPa. This drop represents a reduction in pressure by nearly half.

Understanding how pressure changes with altitude is important in aviation, as it affects aircraft performance, engine efficiency, and pilot physiology. The actual pressure at a specific altitude can vary based on factors like temperature and weather conditions, but the general guideline is that, at 18,000 feet, pilots can expect the pressure to be around 50% of what it is at sea level, which is critical knowledge when flying and in operational planning.