how to figure weight of concrete

tedregentin · Jun 8, 2019

I am making 4 weights from 3 inch pvc pipe. The weights need to be 25 pounds each. Can anyone tell me how long each pipe will need to be to have the correct weight? I am sure there is some kind of formula for this.
Thanks, TEd

Russ from MN · Jun 8, 2019

I think concrete weighs about 150 pounds per cu ft.

Steve@Advance · Jun 8, 2019

I come up with about 39.5" long.

That's the weight of the concrete, might deduct an inch or so for the weight of the pipe and caps.

Janicholson · Jun 8, 2019

Adding to Steve's idea, make the pipes 42 or so, cap the far end, and fill them with ready-mix while on a scale. with the end cap and hook on the scale as well. Jim

MarkB_MI · Jun 8, 2019

OK, the first thing to do is to figure out the volume per inch of your 3 inch ID pipe. As you learned in high school geometry, you can calculate the volume of a solid such as a cylinder by multiplying its cross-sectional area by its volume. And the cross section of a cylinder is a circle, whose area is πr2. Therefore, the volume per inch of a 3 inch ID pipe is:

π(1.5)2 = 7 in3

As Russ pointed out, concrete weighs about 150 lbs/ft3. But we need to convert that to pounds per cubic inch. There are 144 cubic inches per cubic foot.

150 lb/ft3 ÷ 144 in3/ft3 = 1 lb/in3

Now we calculate how many cubic inches are required to make a 25 pound weight.

25 lb ÷ 1 lb/in3 = 25 in3

So we need 25 cubic inches of concrete per weight. And we calculated that the pipe has a volume of 7 cubic inches per linear inch. So:

25 in3 ÷ 7 in3/in = 8.3 inches

Traditional Farmer · Jun 8, 2019

Concrete varies in weight per yard depending on what aggregates are used that is why its priced and sold by the yard a volume measurement instead of being sold by the ton.

MarkB_MI · Jun 8, 2019

I made a dumb mistake. There are 1728 cubic inches per cubic foot, NOT 144!

So the weight per cubic inch is .087 lb/in3

Which means we need 288 cubic inches of concrete

Which works out to 41 linear inches.

john in la · Jun 8, 2019

I figure it a little different.

Russ says concrete is 150 lbs per cu ft.
You want 25 lbs so that is 1/6 of a cu ft.

Now we need to figure the volume of your pipe per inch.
Radius x radius x height x pie
1.5 x 1.5 x 1 x 3.14 = 7.065
So you have 7.065 cu in per inch of pipe.

1728 cu inches in a cubic foot and you need 1/6
1728 / 6 = 288 cu inches

So you need 288 cu inches to make 25 lbs and your pipe holds 7.065 cu inches per inch.
288 / 7.065 = 40.764
So your pipe needs to be 40.764 inches long or just over 40 3/4 inches.

Check Break · Jun 9, 2019

(quoted from post at 19:23:38 06/08/19) Concrete varies in weight per yard depending on what aggregates are used that is why its priced and sold by the yard a volume measurement instead of being sold by the ton.

You can do all the math you want but you're wasting your time for the reason stated above. Aggregate weight varies according to its specific gravity and water content. If you need exactly 25lbs and you don't know the weight of your components best you use the scale as suggested above and add enough weight so that you have 25lbs net when the water bleeds off.

By the time you figure out how to do things right, it will be cheaper to use steel for your weights.

Tramway Guy · Jun 9, 2019

Yes, concrete is usually 150 lb/cubic foot. But it can be higher. Aggregate with high iron content such as found in the Adirondacks can result in weights as high as 162 lbs/cubic foot.

Sometimes you can ask the concrete company and they will tell you.

Traditional Farmer · Jun 9, 2019

I worked at a concrete ready mix and block plant for 25 years,certified by the State of VA to batch and dispatch for the state.We could batch concrete that varied from a little over 3000 lbs a yard up to 4400 lbs a yards depending on aggregates,cement,fly ash etc used in the mix on hand all the time.Also used numerous special mixes for various jobs.There is no set weight for concrete per cubic foot or cubic yard.

Sean Feeney · Jun 9, 2019

Must be why name is iron clad in glens falls, I never knew that

Russ from MN · Jun 9, 2019

Yes, when the Romans built the Pantheon 1800 years ago they used heavy solid aggregate towards the bottom of the dome and lighter volcanic rock near the apex. I did not do that when I built mine!

DR. EVIL · Jun 9, 2019

I hauled readymix concrete for three summers in college. Great summer job! We used 3800# per cubic yard but you check the internet and they say 4050# so the weight comes out evenly to 150# per cubic yard. You figure the empty weight of the trucks I drove, the weight of 7 yards of concrete, plus the 100 gallons of water for clean-up and the 3800# is really REALLY close.

Traditional Farmer · Jun 9, 2019

I saw some Pumice aggregate from Colorado once that was unreal how light it was,solid white.

Stephen Newell · Jun 9, 2019

At 3" diameter I get 2.454 lbs. per inch. That comes to a little less than 10 1/4" for 25 lbs.

Crazy Horse · Jun 9, 2019

It would be interesting to know what you are using the weights for. Is your application designed to use horizontal or vertical weights? If vertical, it leaves you a lot more options for getting exactly to 25 pounds with loose metal fill or even aggregate fill inside the pipe.

tedregentin · Jun 9, 2019

My wife does Saturday market and she has a four post awning over the booth. They require that she have a 25 pound weight at each corner. Right now I have four five gallon buckets. They are difficult to use.

dpendzic · Jun 9, 2019

use 150 LB per cubic foot---5 gallon = 0.668 cf-===100 lbs

dpendzic · Jun 9, 2019

150 # per cubic foot is the accepted standard for designing a concrete structure---you have to start somewhere when you have no idea where the concrete is coming from---there is usually enough of a FOS to compensate for the differences in weight

Jim.ME · Jun 9, 2019

A 1" x 9" x 10" (90 cubic inches at .2904 lb. Per cu.in.) steel plate will give you approximately 26 pounds. A lot more compact than 41" of 3" pipe.

Crazy Horse · Jun 9, 2019

OK so 25 pounds at least .... but could you have 30 or 35 pounds? I suspect that would be fine?

how to figure weight of concrete

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