Earth Horizon Distance & Curvature Calculator
Calculate distance to the true geometric horizon, atmospheric refraction line-of-sight, and Earth curvature drop in miles, kilometers, and nautical miles.
Calculated Results
Frequently Asked Questions
What is the formula for distance to the horizon?
The geometric horizon distance formula is: d ≈ √(2 × R × h), where R is Earth's mean radius (approx. 3,959 miles). For observer eye height h in feet, the formula simplifies to: Distance in Miles ≈ 1.225 × √h (or 1.32 × √h including standard atmospheric refraction).
Why does atmospheric refraction make the horizon look farther away?
Temperature and air pressure gradients in Earth's atmosphere bend light rays slightly downward toward Earth's surface. This refraction allows observers to see roughly 8% farther than pure geometric vacuum line-of-sight.
What is the rule for Earth's curvature drop?
Over short distances, Earth's curvature drops at approximately 8 inches multiplied by the distance in miles squared: Drop (inches) ≈ 8 × d². At 3 miles, curvature drop is 8 × 9 = 72 inches (6 feet).
How far can you see from an airplane at 35,000 feet?
From a passenger jet cruising at 35,000 feet, the horizon is approximately 230 to 248 miles away, encompassing a circular visible ground area of nearly 180,000 square miles.