# Why are manhole covers round? **URL:** \ **Category:** In My Humble Opinion\ **Created:** [June 22, 2002, 5:05am UTC](https://boards.straightdope.com/t/why-are-manhole-covers-round/115404 "2002-06-22T05:05:26Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![chula](https://avatars.discourse-cdn.com/v4/letter/c/a4c791/32.png) [@chula](https://boards.straightdope.com/u/chula)\ **Post date:** [June 22, 2002, 5:05am UTC](https://boards.straightdope.com/t/why-are-manhole-covers-round/115404/1 "2002-06-22T05:05:26Z")
This was a question on a trivia quiz in a bar I frequent. I believe the answer they gave was wrong, and I want to see if the Dopers know the answer. Questions that you already know the answer to can go in IMHO, no? ---
**Author:** ![Mr.Cynical](https://avatars.discourse-cdn.com/v4/letter/m/ee59a6/32.png) [@Mr.Cynical](https://boards.straightdope.com/u/Mr.Cynical)\ **Post date:** [June 22, 2002, 5:07am UTC](https://boards.straightdope.com/t/why-are-manhole-covers-round/115404/2 "2002-06-22T05:07:57Z")
So that they can’t fall into the manhole. Next. ---
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [June 22, 2002, 5:14am UTC](https://boards.straightdope.com/t/why-are-manhole-covers-round/115404/3 "2002-06-22T05:14:25Z")
Cecil knows, sort of. [http://www.straightdope.com/classics/a1\_247a.html](http://www.straightdope.com/classics/a1_247a.html) > [@](#): > > We cannot entirely discount the possibility that the covers are round because someone at the dawn of modern civil engineering discovered he could draw them by tracing around the outside of a penny. ---
**Author:** ![TheOnlySaneOne](https://avatars.discourse-cdn.com/v4/letter/t/67e7ee/32.png) [@TheOnlySaneOne](https://boards.straightdope.com/u/TheOnlySaneOne)\ **Post date:** [June 22, 2002, 5:30am UTC](https://boards.straightdope.com/t/why-are-manhole-covers-round/115404/4 "2002-06-22T05:30:11Z")
Because the holes themselves are not square or rectangular? ---
**Author:** ![chula](https://avatars.discourse-cdn.com/v4/letter/c/a4c791/32.png) [@chula](https://boards.straightdope.com/u/chula)\ **Post date:** [June 22, 2002, 5:47am UTC](https://boards.straightdope.com/t/why-are-manhole-covers-round/115404/5 "2002-06-22T05:47:56Z")
Damn. I guess since I screwed up I didn’t remember seeing it in the archives, I should give up on this thread and give away what I was getting at. The correct answer is “because the manholes are round.” No joking. All this business about rectangles and triangles addresses the question “why are manholes round?” The question was “why are the _covers_ round?” ---
**Author:** ![chula](https://avatars.discourse-cdn.com/v4/letter/c/a4c791/32.png) [@chula](https://boards.straightdope.com/u/chula)\ **Post date:** [June 22, 2002, 5:50am UTC](https://boards.straightdope.com/t/why-are-manhole-covers-round/115404/6 "2002-06-22T05:50:29Z")
Good, someone got it right, before I got around to posting it. **TheOnlySaneOne** wins! ---
**Author:** ![lno](https://avatars.discourse-cdn.com/v4/letter/l/a8b319/32.png) [@lno](https://boards.straightdope.com/u/lno)\ **Post date:** [June 22, 2002, 2:12pm UTC](https://boards.straightdope.com/t/why-are-manhole-covers-round/115404/7 "2002-06-22T14:12:35Z")
“Why are manholes round,” then? Well, because the manhole _covers_ are round, obviously. Otherwise they wouldn’t fit. And the eternal question lives on – which came first, the manhole or the cover? [sub]yes, I know, I’ll stop.[/sub] ---
**Author:** ![Pushkin](https://avatars.discourse-cdn.com/v4/letter/p/ee59a6/32.png) [@Pushkin](https://boards.straightdope.com/u/Pushkin)\ **Post date:** [June 22, 2002, 2:29pm UTC](https://boards.straightdope.com/t/why-are-manhole-covers-round/115404/8 "2002-06-22T14:29:45Z")
> [@](#): > > \*Originally posted by Mr. Cynical \* > \*\*So that they can’t fall into the manhole. > > Next. \*\* True, I’ve spent about a week hauling them up for the company I work for. Course its not like we get the proper equipment for hauling them up. The rectangular/square ones are a bugger when they slip, especially if they’re the sort that split into two triangles with only one point to hold onto them with lifting rods :rolleyes: ---
**Author:** ![white-tigeress](https://avatars.discourse-cdn.com/v4/letter/w/f475e1/32.png) [@white-tigeress](https://boards.straightdope.com/u/white-tigeress)\ **Post date:** [June 22, 2002, 4:40pm UTC](https://boards.straightdope.com/t/why-are-manhole-covers-round/115404/9 "2002-06-22T16:40:54Z")
So they fit the circular hole and then you dont fall in the ground. COuld you honestly imagine a triangular one?? ---
**Author:** ![TJdude825](https://avatars.discourse-cdn.com/v4/letter/t/dec6dc/32.png) [@TJdude825](https://boards.straightdope.com/u/TJdude825)\ **Post date:** [June 23, 2002, 7:13pm UTC](https://boards.straightdope.com/t/why-are-manhole-covers-round/115404/10 "2002-06-23T19:13:48Z")
there is another shape that is wide enough not to fall in, called a Reuleaux triangle, and here is a picture of it… [http://www.maa.org/mathland/10\_21\_fig1.gif](http://www.maa.org/mathland/10_21_fig1.gif) I don’t know if I did the img tag correctly, so just go to [this page](http://www.maa.org/mathland/mathland_10_21.html) if the image doesn’t show up, or if you want more information about the shape. -TJdude825 ---
**Author:** ![bouv](https://avatars.discourse-cdn.com/v4/letter/b/bc8723/32.png) [@bouv](https://boards.straightdope.com/u/bouv)\ **Post date:** [June 23, 2002, 7:43pm UTC](https://boards.straightdope.com/t/why-are-manhole-covers-round/115404/11 "2002-06-23T19:43:04Z")
Having taken a engineering design course, we actually listed as many reasons as possible why the cover (and, subsequently, the hole) are round: So the cover won’t fall in Minimum amount of material for the amount of space Easy to make Easy to transport (they can stack nicely on top, but not as easy as squares, I’ll give you that) Easy to move out of the way (they roll) Easy to construct from a manufactoring viewpoint Sharp corners are dangerous This is a truncated list, as we had many more reasons. But you can see that round things are better for a multitude of reasons. ---
**Author:** ![stankow](https://avatars.discourse-cdn.com/v4/letter/s/cdc98d/32.png) [@stankow](https://boards.straightdope.com/u/stankow)\ **Post date:** [June 23, 2002, 7:49pm UTC](https://boards.straightdope.com/t/why-are-manhole-covers-round/115404/12 "2002-06-23T19:49:31Z")
> [@](#): > > \*Originally posted by chula \* > \*\*The correct answer is “because the manholes are round.” No joking. All this business about rectangles and triangles addresses the question “why are manholes round?” The question was “why are the _covers_ round?” \*\* I disagree. Since the cover is the operating concern here, the reason the cover is round is because it’s the shape that won’t fall into a round manhole. The shape of the manhole doesn’t matter at all, except what will allow the least chance of a cover filling in. You can’t define the equation (round manhole cover = unable to fall into manhole) without including the “manhole cover” part. ---
**Author:** ![Kalashnikov](https://avatars.discourse-cdn.com/v4/letter/k/2bfe46/32.png) [@Kalashnikov](https://boards.straightdope.com/u/Kalashnikov)\ **Post date:** [June 23, 2002, 10:57pm UTC](https://boards.straightdope.com/t/why-are-manhole-covers-round/115404/13 "2002-06-23T22:57:17Z")
> [@](#): > > \*Originally posted by white-tigeress \* > \*\*So they fit the circular hole and then you dont fall in the ground. COuld you honestly imagine a triangular one?? \*\* Sure I can, we have triangular covers (and holes) here in New England. They wouldn’t fall through the holes either. ---
**Author:** ![sward](https://avatars.discourse-cdn.com/v4/letter/s/51bf81/32.png) [@sward](https://boards.straightdope.com/u/sward)\ **Post date:** [June 24, 2002, 2:50am UTC](https://boards.straightdope.com/t/why-are-manhole-covers-round/115404/14 "2002-06-24T02:50:13Z")
With a round cover, it does not have to be aligned precisely to fit. Any way you lay it, it will fit. If it were square, or another shape, it would have to be aligned perfectly to fit.