Q&A for How to Work Out the Circumference of a Circle

Double the radius. That's the diameter. Multiply the diameter by pi. That's the circumference. Multiply the circumference by five. That's how far the wheel travels in five revolutions.

Assuming the diameter of the circle is to be one meter, multiply the diameter by pi. That means the rope would have to be 3.14 meters long.

The total perimeter is the diameter (twice the radius) plus half the circumference of the full circle. So it's 12 + (12π / 2) = 12 + 6π = 30.85 cm.

Divide the circumference by pi.

Assuming you cannot expose the remainder of the tank's rim, you can come up with an approximate circumference by inscribing in the soil a circle based on the exposed curvature. Then use a yardstick or other long straightedge to run along the circle to measure its length.