Atmospheric Pressure & Altitude Calculator

Atmospheric Pressure Guide

The Barometric Formula

P(h) = P₀ × (1 − Lh/T₀)^(gM/RL). Simplified for the troposphere (up to ~11km): P ≈ P₀ × exp(−h/H), where H = scale height ≈ 8,400m. Standard sea level: P₀ = 101,325 Pa = 1013.25 hPa = 1 atm. Pressure decreases by about 12% per 1,000m near sea level. At 5,500m (Everest base camp): pressure ≈ 500 hPa, half sea level. At 8,848m (Everest summit): pressure ≈ 314 hPa, about one-third sea level. The 'death zone' begins at approximately 8,000m where oxygen partial pressure becomes too low to sustain hum

Boiling Point and Altitude

Water boils when vapour pressure equals atmospheric pressure. At sea level (101kPa): water boils at 100°C. At 1,500m altitude (84kPa): water boils at approximately 94.5°C. At 3,000m (70kPa): 89.8°C. At 5,500m (53kPa): 83°C. Higher altitude cooking implications: water boils at lower temperature → food takes longer to cook. Baking requires adjustment — reduce leavening, increase liquids, increase temperature. Pressure cookers solve this — they seal and increase internal pressure, raising the boili

Air Density at Altitude

Air density ρ = P / (RT). Where R = specific gas constant for air = 287 J/(kg·K), T = temperature in Kelvin. At sea level, 15°C: ρ = 101325 / (287 × 288.15) = 1.225 kg/m³. At 3,000m, 5°C: ρ ≈ 0.91 kg/m³. Reduced air density at altitude affects: aircraft performance (lower lift, reduced engine output). Athletic performance — distance running requires more breaths per minute; sprinting is slightly faster due to reduced drag. Aerobic capacity drops approximately 1% per 100m above 1,500m. Altitude t

Effective Oxygen Percentage

Sea level air composition: 21% oxygen. This does NOT change with altitude. What changes is the partial pressure: total pressure × 21%. At sea level: pO₂ = 21.3 kPa. Mount Everest: pO₂ ≈ 6.6 kPa (about 31% of sea level oxygen availability). This is why oxygen masks are needed above approximately 4,500m for many people. Altitude sickness: typically appears above 2,400m. Acute mountain sickness (AMS): headaches, nausea, fatigue. Resolves in 24-48 hours with acclimatisation or descent. High altitude