Atmospheric Pressure at Altitude Calculator

Atmospheric pressure decreases with increasing altitude because there is less air above to exert downward force. This relationship is described by the barometric formula, which is fundamental to aviation, meteorology, and understanding how altitude affects human physiology.

The barometric formula (troposphere, 0-11 km): P = P₀ × (1 - (L × h) / T₀)^(g × M / (R × L))

Where:

• P₀ = sea level standard pressure (101,325 Pa or 1013.25 hPa)
• L = temperature lapse rate (0.0065 K/m)
• h = altitude above sea level (meters)
• T₀ = sea level standard temperature (288.15 K or 15°C)
• g = gravitational acceleration (9.80665 m/s²)
• M = molar mass of dry air (0.0289644 kg/mol)
• R = universal gas constant (8.31447 J/(mol·K))

The simplified exponent g×M/(R×L) equals approximately 5.2559.

Rule of thumb: Pressure decreases by approximately 12 hPa (millibars) for every 100 meters of elevation gain near sea level. This rate decreases at higher altitudes because the air becomes less dense.

Pressure at notable altitudes:

• Sea level: 1013.25 hPa (760 mmHg, 29.92 inHg)
• Denver, Colorado (1,609 m): ~835 hPa (about 83% of sea level)
• Mount Fuji summit (3,776 m): ~636 hPa (about 63%)
• Mount Everest summit (8,849 m): ~314 hPa (about 31%)
• Cruising airplane (10,668 m): ~237 hPa (about 23%)

Human physiology effects: As altitude increases, the partial pressure of oxygen decreases proportionally. At 2,500 meters (8,200 feet), most people begin to notice the reduced oxygen. At 5,500 meters (18,000 feet), altitude sickness becomes common without acclimatization. Above 8,000 meters (26,000 feet) is called the “death zone” where human survival without supplemental oxygen is very limited.

Boiling point of water: Lower atmospheric pressure means water boils at a lower temperature. At sea level, water boils at 100°C (212°F). At 2,000 meters, it boils at approximately 93°C (199°F). At Mount Everest’s summit, water boils at about 70°C (158°F), making it difficult to cook food properly.

Aviation applications: Pilots use pressure altitude extensively. The altimeter in aircraft works by measuring atmospheric pressure and converting it to altitude. Standard pressure (1013.25 hPa) is set above a certain altitude (transition altitude), and local pressure corrections are used below that altitude for accurate height readings.