Human Lung Surface Area: Why Alveoli Cover a Tennis Court

If all ~480 million alveoli in adult lungs were flattened, their total surface area would be ~100 m² (1,076 ft²)—roughly the size of a tennis court.

Why So Large?

• Gas exchange (O₂ in, CO₂ out) occurs by diffusion across the alveolar-capillary membrane.
• Diffusion rate ∝ surface area × Δconcentration / thickness.
• Massive area + ultra-thin barrier (0.5 µm) + dense capillary network = efficient exchange at rest and during exercise.

Clinical Relevance

Emphysema destroys alveolar walls → surface area ↓ → dyspnea, exercise intolerance. Preserving lung structure preserves function.