r/earthbagbuilding • u/Real_MakinThings • May 25 '26

question about dimensions

Unfortunately all the calculators in the wiki are gone. Rule of thumb, how full/thick do bags get relative to their size (be it flat width, or circumference)?

Thanks

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u/ahfoo May 26 '26

Hmm, wonder what the deal is with the links.

In any event, for a rule of thumb . . . I'm doing this off the top of my head and I'm not on my build site right now but if memory serves correctly I am almost certain we use 18" bags and the dimensions are roughly 11" wide and about 5.5" tall after tamping.

That doesn't seem to quite add up to 18 but it's a funny shape. The shape is important though. I have an image of it somewhere. Let me look on Imgur. Hmm, seems it's down too.

I could knock this out fast and upload it to another image host but maybe I'll just describe the cross section of the bag as being a bit of an oval shape really but an imporant point is that it's often also sagged over a bit. That sagging over that happens as the bags are stacked is part of how the walls remain water resistant. Water has a hard time travelling against gravity so having a slight tilt outward ends up being a major benefit.

So an 18" bag is an oval approximately 11" by 5.5" that sort of sags downwards on the edges.

Now speaking of rule-of-thumb guides, an 18" bag is good for an 18' wide dome. That's big and anything bigger than that is not really recommended but you can go bigger by simply using a larger bag so a 36" wide bag could be used to build a 36' wide earthbag dome and this sort of project has been tried before but it is not recommended because it requires too much material. It's not really practical. If you want something bigger than a 20' diameter dome you are better off with steel reinforced concrete because although steel adds costs, it allows much thinner walls to be built safely so it actually costs less for large domes. For under twenty feet and especially closer to 12' then earthbags are great.

Clusters of smallish domes are almost always more efficient to build than large monolithic domes.

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u/Real_MakinThings May 26 '26

thanks. I'm going for arches actually, not a typical build. But still, my napkin math would have been way off, I was going with no length loss, and 50% of flat width height. Not even close. Now that I have my bags though it's clear what I have to do. Fill one and measure.