Earth Curve Calculator 2026
Calculate exactly how much Earth’s surface curves over any distance. Find the geometric drop, hidden height behind the horizon, and horizon distance — with optional atmospheric refraction correction.
Distance & Observer Settings
Enter your distance and optional observer height for a complete curvature analysis
The distance along the Earth’s surface from the observer to the target
Height of your eyes above sea level. Used to calculate the maximum visible horizon distance.
Height of the distant object (e.g. a building or mountain). Used to compute how much is visible above the horizon.
The mean radius is accurate for most calculations. Use polar/equatorial for precision work near the poles or equator.
Curvature Results
Geometric drop, hidden height, and horizon distance
Enter a distance above and click Calculate Earth Curvature to see the geometric drop, hidden height, and horizon limit.
Earth Curvature at a Glance
Geometric drop values (without refraction) for common distances. The drop is not linear — it grows with the square of the distance. Refraction typically reduces the effective drop by about 13%.
| Distance | Geometric Drop | Drop (with refraction) | Typical Example |
|---|---|---|---|
| 1 km | 0.08 m | 0.07 m | Short-range surveying |
| 5 km | 1.96 m | 1.71 m | City-to-suburb line of sight |
| 10 km | 7.85 m | 6.83 m | Typical radio link |
| 25 km | 49.0 m | 42.6 m | Coastal photography |
| 50 km | 196 m | 171 m | Mountain-to-mountain |
| 100 km | 785 m | 683 m | Long-range antenna links |
| 500 km | 19,600 m | 17,052 m | Intercontinental visibility |
Earth Curvature FAQ
Everything you need to understand Earth’s curvature calculations, from the basic formula to real-world surveying and photography applications.
The Earth’s surface curves approximately 8 inches (20 cm) per mile squared, or about 7.98 cm per kilometre squared. This means over 1 km the drop is roughly 8 cm; over 10 km it is about 7.8 m; and over 100 km it is around 785 m. The relationship is not linear — it scales with the square of the distance.
Hidden height (also called obscured height) is the portion of a distant object that is hidden below the horizon due to Earth’s curvature. It depends on the distance to the object and the observer’s eye height above sea level. A taller observer can see further and therefore sees less of the object hidden. Our calculator computes hidden height accounting for observer elevation.
Atmospheric refraction is the bending of light as it passes through layers of air with different densities. In standard atmospheric conditions, refraction bends light slightly downward, effectively making the Earth appear less curved than it is geometrically. A standard refraction coefficient of approximately 0.13 (sometimes expressed as 7/6 effective Earth radius) is commonly used in surveying and is included as an optional correction in our calculator.
The distance to the horizon depends on your eye height above sea level. The formula is approximately d = √(2Rh), where R is Earth’s radius (6,371 km) and h is your eye height in the same units. At sea level with eyes at 1.7 m, the horizon is about 4.7 km away. From a cliff at 100 m, it extends to about 35.7 km.
Radio engineers use Earth curvature calculations to determine whether a line-of-sight link is achievable between two antenna masts — especially for microwave and point-to-point links where obstruction by the horizon is a critical factor. Photographers and filmmakers use it to work out how much of a distant landmark or ship is hidden below the horizon, and to plan long-distance shots accurately.