Why Are Manhole Covers Round?

Manhole covers are round because the hole is round. Thank you for stepping by and reading this magnificent article. I hope you enjoyed it. Just kidding.

No really, i know they are an overlooked feature of our everyday life but have you ever wondered why usually manhole covers are round?

This question became very popular when Microsoft HR people were using it in job interviewsSo, what would be your answer? Why are they around? Let’s find out. (the article continues after the ad)

Manhole covers go back to the ancient Romans. Way back before the time of Christ, Romans were using square sewer grates that were made of lime sandstone. But as years went by, people realized that square wasn’t actually the best shape. So, when trying to find the perfect design, they figured that a round shape manhole works best for various reasons:

  • It’s way easier digging a circular hole than a square hole
  • A round shape is the most efficient and strongest shape when it comes to resisting the compression or the earth around it
  • A round cover cannot fall through the opening, no matter how you position it. On the other hand, a square cover will fall in if you place it diagonally
  • Circular covers don’t need to be precisely aligned when they are placed on the opening
  • I don’t know if you’ve ever tried to lift one, but these things are quite heavy. By having them round, one can easily roll them to their holes

Of course, we’ve come a long way since the ancient Roman times. Manhole covers now need to be strong and heavy enough so that hundreds of cars can pass over them every day without a problem, new materials have been introduced, production methods have changed etc. The benefits of the round shape manhole though are pretty much the same as they were many many years ago.

And this is why, manholes (and their covers) are usually round.

If you like what you read, then you will definitely love this one: The Simple Reason Why Swiss Cheese Has Holes In It      



Photo: Wikimedia
Photoshop: I’m A Useless Info Junkie
Sources: Job Interview Question And Answer: Why Are Manhole Covers Round? | Why is a manhole cover round? A Microsoft interview question | Ask a Science Teacher: 250 Answers to Questions You’ve Always Had About How Everyday Stuff Really Works