The moving sofa math problem: still unsolved 50 years later

Originally published at:


Find an electric monk…


How well I remember trying to move a friend’s “hell desk” around a corner and down the stairs…


This is not the optimal sofa. The optimal sofa is optimized for sitting on. It is comfy, yet durable. It is supposed to be difficult to move; that’s how you know it’s a sofa.



The rest of us living in the real world know that the best way to move a sofa around a corner is to stand it on its end. For a real challenge, move a sofa up a flight of stairs in a hallway with a 90 degree corner.

For extra credit, move a sleeper sofa up the same hallway stairs.


Decades ago, I had the greatest couch a frequent mover could ask for…The arms bolted on.

Flip the couch over.

Peel back the velcro attached fabric.

Remove the three bolts from each arm. (Note - Standard bolts that you can buy from any hardware store. Nothing exotic)

Move the arms. Move the body. Re-assemble.

Without the arms, it would go through a normal doorway vertically. No doorway, nor flight of stairs, nor wonky hallway would impede that couch from getting to its final spot.

Sadly, its fabric was light colored and after a ill place glass of wine…it was never the same.



I have a similar couch. The arms bolt on. We got it up a flight of stairs and through a door by taking the arms off beforehand. However, I just barely go through a normal doorway vertically, and this thing is big enough for me to sprawl out on, so it still needed to be angled through doorways.


remember that laurel and hardy piano movers caper…
you hum it and I’ll play it


Old story allegedly from (I think) the Royal Albert Hall in London: before committing to buying a new concert grand piano, they needed to be certain it would fit down a corridor with a bend in it. So they asked their in-house carpenter to make a full-size model for them to test. He did. He couldn’t get it out of the workshop.


C’mon, cite where you got the idea to post this: hmmmmmm

I wonder if there are singularities in the problem that make exact solutions impossible? The sharp corner of the hallway makes me wonder.

We have a one piece hutch my grandfather made during WWI (he was a German professor and apparently he had to do something else during the war, because teaching German was Not Done). Anyway, being one piece it has many of the same problems. Turning it on its side helps.


I once worked as a mover. Regular sofas were easy, sleeper sofas were morale killers.

And yeah, duh, stand it on its end, solved, was there a prize attached to this problem?


What kinda unconventional & weird-assedly-shaped sofa is that?

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Apparently those posing the problem never heard of sectionals.


BB often credits Reddit with their embracing of a story idea. So they miss a few…

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Prof. Dan Romik at UC Davis has a very nice writeup of this problem on his web page. This includes some recent research of his on a variant of the problem, in which the sofa has to be able to navigate both a left turn and a right turn in the corridor. He includes STL files so you can 3D print your own sofa.

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Sleeper sofas are morale killers to sleep on too.

Last time I moved I finally hired movers for the first time. I hadn’t before because I was under the impression they were prohibitively expensive. Nope, best $300 I ever spent. I tell you what, I am never moving my own furniture again (unless I’m just rearranging a room.)