Eratosthenes used a simple formula that relates the proportionality proportionality of distance on the meridian (d ) and the difference in latitude (α) to the relation between the perimeter (P ) and the angle of the circle (360º):

Earth's perimeter can therefore be calculated by the formula

We can also calculate Earth's radius using the formula

CONFIRM YOUR CALCULATIONS

To use the calculator to confirm your calculations fill the Distance to the Tropic of Cancer and Shadow at top fields (by this order) and then press the "Submit" button