Flat vs. Round Earth Calculator

Compare visual observations and curvature effects on a flat vs. spherical Earth.

Observation Data

Observer Height (m)

Distance to Object (km)

Target Object Height (m)

Comparison Results

Enter parameters to see comparison

About this calculator

Quick Reference

R (Earth Radius)6,371 km

Horizon Formulad = sqrt(2Rh)

Curvature Drop~8 inches / mile²

Sea Level Sight~4.7 km at 1.7m height

Overview

This tool calculates how much of an object would be hidden by Earth's curvature compared to a hypothetical flat plane.

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Pro Tips

Standard atmospheric refraction makes objects appear slightly higher than they are (added ~7/6 multiplier to radius).
On a Flat Earth, you could theoretically see infinitely far if the air was perfectly clear.
The horizon is mathematically where the line of sight is tangent to the sphere.

Fun Facts

"The '8 inches per mile squared' rule is a common approximation for Earth's curvature drops."
"Cargo ships disappear bottom-first as they move away—consistent with a curved surface."
"Atmospheric refraction can sometimes create 'mirages' that make distant objects visible even when they should be below the horizon."

Formula: d = v(2Rh + h²)