# How much does one cubic FOOT of concrete weigh? **URL:** \ **Category:** Factual Questions\ **Created:** [June 25, 2005, 8:23pm UTC](https://boards.straightdope.com/t/how-much-does-one-cubic-foot-of-concrete-weigh/309827 "2005-06-25T20:23:20Z")\ **Posts on this page:** 9\ **Page:** 2
**Author:** ![Valgard](https://avatars.discourse-cdn.com/v4/letter/v/7feea3/32.png) [@Valgard](https://boards.straightdope.com/u/Valgard)\ **Post date:** [June 28, 2005, 12:52am UTC](https://boards.straightdope.com/t/how-much-does-one-cubic-foot-of-concrete-weigh/309827/21 "2005-06-28T00:52:38Z")
> [@Can Handle the Truth](#): > > Architectural designer/engineer weighing in. > > In my structural calculations I use 150 lbs per cubic foot for concrete. Second this value from former civil/structural engineer. That’s what we used in every single concrete design class I took. And before you ask that’s a good value for both unreinforced and reinforced concrete 🙂 ---
**Author:** ![lostronin](https://avatars.discourse-cdn.com/v4/letter/l/a4c791/32.png) [@lostronin](https://boards.straightdope.com/u/lostronin)\ **Post date:** [June 28, 2005, 1:44am UTC](https://boards.straightdope.com/t/how-much-does-one-cubic-foot-of-concrete-weigh/309827/22 "2005-06-28T01:44:45Z")
165lbs approx. 7.4805 gallons per cubic foot 8.33 pound per gallon thus a cubic foot of water weighs 62.31 lbs aggregate producers typically mine and crush limestone for use in concrete and asphaltic concrete. Specific gravity of the raw mineral (sand and gravel) is typically 2.65, give or take. Cement is a little lighter but there isn’t much compared to aggregate content. 7.4805x8.33x2.65 is as close as you’ll get without factoring in dry cement SG that of course does not take into consideration the weight of rebar if used ---
**Author:** ![FordPrefect](https://avatars.discourse-cdn.com/v4/letter/f/e99b99/32.png) [@FordPrefect](https://boards.straightdope.com/u/FordPrefect)\ **Post date:** [June 28, 2005, 2:03am UTC](https://boards.straightdope.com/t/how-much-does-one-cubic-foot-of-concrete-weigh/309827/23 "2005-06-28T02:03:30Z")
> [@lostronin](#): > > 165lbs approx. > > 7.4805 gallons per cubic foot > 8.33 pound per gallon > thus a cubic foot of water weighs 62.31 lbs > > aggregate producers typically mine and crush limestone for use in concrete > and asphaltic concrete. Specific gravity of the raw mineral (sand and gravel) > is typically 2.65, give or take. Cement is a little lighter but there isn’t much compared to aggregate content. > > 7.4805x8.33x2.65 is as close as you’ll get without factoring in dry cement SG > > that of course does not take into consideration the weight of rebar if used Don’t forget the embedded air, and also that most (I think) of the water will evaporate from the concrete after catalyzing the cement powder ---
**Author:** ![tremorviolet](https://avatars.discourse-cdn.com/v4/letter/t/e47774/32.png) [@tremorviolet](https://boards.straightdope.com/u/tremorviolet)\ **Post date:** [June 28, 2005, 2:38am UTC](https://boards.straightdope.com/t/how-much-does-one-cubic-foot-of-concrete-weigh/309827/24 "2005-06-28T02:38:33Z")
> [@FordPrefect](#): > > Don’t forget the embedded air, and also that most (I think) of the water will evaporate from the concrete after catalyzing the cement powder Not really. The water doesn’t “catalyze” the cement powder; through _hydration,_ water forms chemical bonds with the cement. ([here’s](http://www.olemiss.edu/courses/engr313/engr314/introduction.html) a little CE101 page if you’re interested, this page also has the concrete professors’ favorite refrain: Under no circumstances should the word “cement” be used to refer to the composite product “concrete”. ) So there isn’t a lot of water to evaporate as it’s used during hydration. Wet concrete is essentially the same volume as cured concrete with shrinkage of usually much less than 1%. Which is one reason why it’s such a great building material. So using the standard weight of 150 pounds/cf (which is the weight most engineers use for their calcs, it’s the highest and, therefore, most conservative) for both weight and cured concrete is fine. And enineers usually don’t bother to calculate the weight of the rebar. It’s true steel is 490 lbs/cf compared to concrete’s 150 lbs/cf but you usually use such small amounts of rebar that it’s not worth the time to calculate. ---
**Author:** ![lostronin](https://avatars.discourse-cdn.com/v4/letter/l/a4c791/32.png) [@lostronin](https://boards.straightdope.com/u/lostronin)\ **Post date:** [June 28, 2005, 12:13pm UTC](https://boards.straightdope.com/t/how-much-does-one-cubic-foot-of-concrete-weigh/309827/25 "2005-06-28T12:13:45Z")
> [@FordPrefect](#): > > Don’t forget the embedded air, and also that most (I think) of the water will evaporate from the concrete after catalyzing the cement powder You’re right, didn’t consider entrained air! That accounts for the 150 rule of thumb most engineers use I presume. ---
**Author:** ![FordPrefect](https://avatars.discourse-cdn.com/v4/letter/f/e99b99/32.png) [@FordPrefect](https://boards.straightdope.com/u/FordPrefect)\ **Post date:** [June 28, 2005, 8:32pm UTC](https://boards.straightdope.com/t/how-much-does-one-cubic-foot-of-concrete-weigh/309827/26 "2005-06-28T20:32:44Z")
> [@tremorviolet](#): > > Not really. The water doesn’t “catalyze” the cement powder; through _hydration,_ water forms chemical bonds with the cement. ([here’s](http://www.olemiss.edu/courses/engr313/engr314/introduction.html) a little CE101 page if you’re interested, this page also has the concrete professors’ favorite refrain: Under no circumstances should the word “cement” be used to refer to the composite product “concrete”. ) So there isn’t a lot of water to evaporate as it’s used during hydration. Interesting. So you are referring to the barest, minimum amount of water required to hydrate (not catalyze LSNT) My use of “evaporation” which isn’t quite the right term either for what I meant comes from my experience in concrete construction. After pouring a floor or beam there would be water that would rise to the surface. Admittedly this water would be there because we were using more than the minimum amount of water. (It didn’t really matter since the concrete would still cure to a strength well beyond the engineer’s specs.) ---
**Author:** ![tremorviolet](https://avatars.discourse-cdn.com/v4/letter/t/e47774/32.png) [@tremorviolet](https://boards.straightdope.com/u/tremorviolet)\ **Post date:** [June 28, 2005, 8:54pm UTC](https://boards.straightdope.com/t/how-much-does-one-cubic-foot-of-concrete-weigh/309827/27 "2005-06-28T20:54:22Z")
> [@FordPrefect](#): > > Interesting. So you are referring to the barest, minimum amount of water required to hydrate (not catalyze LSNT) My use of “evaporation” which isn’t quite the right term either for what I meant comes from my experience in concrete construction. After pouring a floor or beam there would be water that would rise to the surface. Admittedly this water would be there because we were using more than the minimum amount of water. (It didn’t really matter since the concrete would still cure to a strength well beyond the engineer’s specs.) Yeah, you have to add a littlemore water than absolutely necessary for workability (particularly with things like beams where you need to make sure the concrete works down around the rebar cage). And it’s true we usually use a pretty conservative concrete strength for our calcs. But you really don’t want to use a whole lot of excess water 'cause it’ll actually decrease the concrete strength. Usually the concrete guys carefully calculate the water to cement ratio (and check it with a slump test which is excatly like it sounds) so you get sufficient workability with the required strength. Here’s a good paragraph from that page I linked above: > [@](#): > > Strength of Concrete > > The strength of concrete is very much dependent upon the hydration reaction just discussed. Water plays a critical role, particularly the amount used. The strength of concrete increases when less water is used to make concrete. The hydration reaction itself consumes a specific amount of water. Concrete is actually mixed with more water than is needed for the hydration reactions. This extra water is added to give concrete sufficient workability. Flowing concrete is desired to achieve proper filling and composition of the forms. The water not consumed in the hydration reaction will remain in the microstructure pore space. These pores make the concrete weaker due to the lack of strength-forming calcium silicate hydrate bonds. Some pores will remain no matter how well the concrete has been compacted. The relationship between the water/cement ratio and porosity is illustrated in Figure 3. ---
**Author:** ![Carnac\_the\_Magnificent](https://avatars.discourse-cdn.com/v4/letter/c/ccd318/32.png) [@Carnac\_the\_Magnificent](https://boards.straightdope.com/u/Carnac_the_Magnificent)\ **Post date:** [June 29, 2005, 1:40pm UTC](https://boards.straightdope.com/t/how-much-does-one-cubic-foot-of-concrete-weigh/309827/28 "2005-06-29T13:40:33Z")
Mant thanks for all the responses. Never thought I’d get so many responses regarding concrete. Imagine if I’d inquired about silicon… ---
**Author:** ![UncleBeer](https://avatars.discourse-cdn.com/v4/letter/u/977dab/32.png) [@UncleBeer](https://boards.straightdope.com/u/UncleBeer)\ **Post date:** [June 29, 2005, 4:57pm UTC](https://boards.straightdope.com/t/how-much-does-one-cubic-foot-of-concrete-weigh/309827/29 "2005-06-29T16:57:18Z")
> [@RM Mentock](#): > > any old fucking rock [LoVeRoCk](http://boards.straightdope.com/sdmb/member.php?username=loverock)? [Previous page](https://boards.straightdope.com/t/how-much-does-one-cubic-foot-of-concrete-weigh/309827.md?page=1)