What is the weight of a cubic yard of water? Would it be 27 times the weight of a cubic foot of water, or am I just confused again? Thanks.

Yes

1685.55492 lbs.

Precisely, thanks.

The density of water varies with temperature and pressure and also any impurites in the water. Under the conditions of 23 degrees Celcius near sea level, a cubic foot of water would weigh about 62 pounds, and thus the cubic yard would be about 1674 pounds.

To keep yourself from being confused, write out the equation with units.

water is about 62.4 lbs/ft^3 so

(62.4 lbs/ft^3) * (3 ft/1 yd)^3 =

(62.4 lbs/ft^3) * (27 ft^3/ 1 yd^3) = 1684.8 lbs/yd^3

If you write it out it’s easy to see how the units cancel out and what you need to multiply by. I’m an engineer with lots o’math behind me but I find that writing out my units keeps me from making obvious mistakes.

Thanks teachers. And it’s fun to learn.

And thanks SDMB.

Wow! six posts in one day ! What the hell took you so long ?

Just curious, would it make any difference if this were fresh water or salt water? Would the salt add to the weight?

In general, salt dissolves in water, which means adding more salt increases the mass (and weight) of the solution but not the volume. So if I’m not mistaken, yes, the salt would add to the weight.

Yes. But I don’t think it makes much of a difference unless you are a fully laden ocean fish boat entering a river to get to port

The salt would add to the weight even at the same volume, because NaCl molecules would be taking the place of lighter water molecules.

I just usually like to lurk and learn.

It wouldn’t affect the volume *at all*? That doesn’t sound right.

This site says the typical specific gravity of ocean water at the surface is around 1.027. IOW, ocean water is 2.7% denser than fresh water.

Water from the Dead Sea is close to fully saturated with salt. Its specific gravity is around 1.16.

A cubic yard is a cubic yard is a cubic yard. :smack:

It’s what you put INTO the cubic yard that is of interest. In salt water, more NaCl, less H2O. Thus, more weight.

Just out of sheer curiosity, why did you use 23*C? I would think that 15* would be the temperature of choice…

Actually its 4*C since that is when water is at its densest. That was the temperature ised when the metric system first was defined (1 cm^3 of water -> 1 gram)

or:

1 cc of water = 1 gram (approx.)

google “convert 1 cubic yard to cc” gives “1 (cubic yard) = 764 554.858 cc”

google “convert 764554.858 grams to pounds” gives “764 554.858 grams = 1 685.55494 pounds”

For practical purposes I’ve always used 8.34 lbs. as the wt. of a gal. of water, and 7.5 cu. ft. per cu. ft.

However I looked it up and the more precise figures are 8.3452 and 7.4805 respectively.

Using those figures, I get 1685.5093 lbs. for a cu. yd. of water. Specific gravity and temp. aside.