How far is the horizon from up there?
The horizon distance grows with the square root of height, which is why climbing twice as high only shows you 41% further.
79% of a from a 50 m lighthouse
20 km is further than 3 of the 8 references on this page.
Reference figures are measurements and are rounded; the unit conversion behind them is exact.
| Reference | Size | Yours ÷ theirs | Note |
|---|---|---|---|
| standing on the beach | 4.9 km | 4.08× | Eye level 1.7 m |
| on a 3 m wall | 6.2 km | 3.23× | |
| from a 10 m lifeguard tower | 11.3 km | 1.77× | |
| from a 50 m lighthouse | 25.3 km | 0.791× | |
| top of the Eiffel Tower | 64.7 km | 0.309× | |
| top of the Burj Khalifa | 103 km | 0.195× | |
| from an airliner at 11 km | 374 km | 1/18.7 | |
| from the ISS at 408 km | 2,294 km | 1/115 |
Worth knowing
- From eye level on a beach the horizon is only 4.9 km away — closer than most people would guess, and the reason ships "sink" as they leave.
- Doubling your height multiplies the horizon distance by 1.41, not 2, because it goes as the square root.
Frequently asked
How far away is the horizon?
Roughly 3.57 times the square root of your eye height in metres, in kilometres. At 1.7 m that is 4.7 km; refraction stretches it to about 4.9 in practice.
Why can you see mountains much further away?
Because the horizon limit applies to the point where your line of sight grazes the surface. Anything tall enough sticks up past it — which is how you can see a peak 200 km away.
How to read this
Figures include the usual allowance for atmospheric refraction, which extends the geometric horizon by about 8%.