Why Are Manholes and Manhole Covers Round?

February 14, 2024

If you’ve ever looked down at your feet while walking around a city, you may have noticed that most manholes and their covers are round. The question of why manholes and their covers are round has become a bit of a cliche, and one that is asked during many job interviews (it even appears in the third edition of The Complete Idiot’s Guide to Job Interviews). The reason that most people ask this question is that there doesn’t seem to be any clear answer, which can make it an opportunity for interviewees to show their creative problem-solving skills.

Despite this, there are actually a few good reasons why manholes and their covers are round, all of which have to do with structure, safety, and efficiency. One of the most common reasons is that a round cover can’t fall into the hole that it covers. This is because the lips that hold the manhole cover in place make the underlying hole smaller than the cover itself, which prevents it from falling in no matter what orientation you put it in, on, or over the hole.

The other main reason why manhole covers are round is that they’re easier to transport, roll, and move about on the ground than their square, rectangular, and oval counterparts. This is because they don’t need to be aligned in any particular direction like their other shapes, and since they’re round, they can be rolled by workers using only their arms. Lastly, circular covers also have less surface area than their square and rectangular counterparts, which means they require less material to produce.


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