Why are manhole covers round?

If you ever looked down the streets carefully, you will found out that most of the manholes and their covers are round in shape. Or maybe you have faced the question in a quiz or a job interview.

Despite all the possible shapes why was a circular shape chosen?

Well, there are several reasons behind it-

  • A circle is the best shape to resist compressive force acting upon it.
  • As a circle is dimensionally symmetrical, it can distribute the weight acting upon it evenly.
  • Circular shapes are easier to manufacture than square, rectangular, oval or any other shapes.
  • Manhole covers are heavy, being round makes them easier to move and handle.
  • Circular covers are not needed to be aligned as on circular frame, and it fits effortlessly.
  • The most important reason behind it is that circular covers can’t fall in the manhole as cut-out of the frame is always smaller than the cover’s size. No matter how you position it the cover is wider than the hole. But, in case of a square, a rectangular or an oval shape, they can fall into the hole if they are aligned diagonally and that could be a nightmare for pedestrians and drivers.

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