Earth Curvature Calculator
The Earth is round, so over a long stretch of flat land or open water the surface falls away from a straight line. This page shows how far it drops over a distance, and how far off the horizon is from a given height.
Both figures are estimates for a smooth, round Earth.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
The drop is roughly the distance multiplied by itself, then divided by twice the Earth's radius, which is about 6,371 kilometres. The answer is how far the surface sits below a straight line from you.
The horizon is roughly the square root of twice the Earth's radius multiplied by your height. Air bends light a little near the ground, so real sight lines reach a bit further than this simple figure.
Worked example
Across 3 mi, the surface drops about 6 ft below a straight line. From a height of 6 ft, the horizon is about 3 mi away.
Questions
Does curvature matter over short distances?
Not much. Over a few hundred metres the drop is well under an inch, so it shows only on long sight lines across lakes or flat fields.
Why can I see further than this height suggests?
Light bends slightly through the air close to the ground, which lets you see a little past the simple geometric horizon.
Does this allow for waves, tides or hills?
No. It uses a smooth, round Earth and a standard radius, and it ignores waves, tides and the land in between.
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