How Much Do Stones Weigh?
This box is about 10 1/8 inches long, 6 1/4 inches wide and about 4 1/4 inches high. It holds about 16 2/3 pounds of mixed tumbled stones.
How Many Pounds of Stone Will I Need?
How many pounds of tumbled stones will you need to use them as ground cover in a potted plant or to fill a decorative jar?
It is very easy to estimate the amount of stone needed if you know the size of the jar and how much the stones weigh in pounds per cubic inch.
This works for small projects such as filling a planter, but it can also be used for estimating how many tons of stone will be needed in a landscaping project.
About ten pounds of mixed tumbled stones will be needed to cover the soil surface in each of these planters to a depth of about two inches. Image © Randy Look, iStockphoto.
Planter: An Easy Example...
Let's say that you have some nice planters like the three in the image at right. You want a colorful layer of tumbled stones on top of the soil in the planter. That will enable you to water the plants without disturbing the soil in the planter. How many pounds of stones will be needed?
Each planter has a soil surface area that is nine inches long and nine inches wide. You want to cover the soil surface about one inches deep with mixed tumbled stones. How many pounds will you need?
Your first job is to calculate how many cubic inches of stone will be needed. This is done by multiplying length x width x depth.
9″ x 9″ x 1″ = 81 inches3
Great! We need 81 cubic inches of stone. How many pounds is that?
Mixed tumbled stones weigh about 0.0618 pounds per cubic inch (or about 107 pounds per cubic foot), and we need 81 cubic inches, so we simply multiply...
81 inches3 x 0.0619 pounds/inch3 = 5.01 pounds
There's our answer! We need about 5 pounds of mixed tumbled stones for each planter. This number is an estimate and it should be fairly close. However, depending upon the size of the stones and the shape and the size of the container in which they will be used, that number could be a little high or a little low. But, it is a reasonable estimate.
About 4 2/3 pounds of mixed tumbled stones will be needed to cover the soil in this pot to a depth of about 1 1/2 inches. Image © Skip ODonnell, iStockphoto.
Round Flower Pot
The amount of stones needed to cover the surface of a round flower pot can easily be calculated. As an example, how many pounds of stone would be needed to cover the soil surface of the flower pot at right to a depth of about 1 1/2 inches?
Our first task is to calculate the soil surface area. The formula for calculating the area of a circle is A = Pi x r2. Pi is equal to approximately 3.14 and our flower pot has an inside radius of 4 inches (a diameter of 8 inches). So by calculation, the surface area is…
3.14 x 4 inches x 4 inches = 50.24 inches2
If we multiply the surface area by the desired depth of coverage the result will be the volume of stones needed.
50.24 inches2 x 1.5 inches = 75.36 inches3
Now to get the weight of the stones needed, we multiply the volume by the density of the stones (0.0619 pounds/inch3).
75.36 inches3 x 0.0619 pounds/inch3 = 4.66 pounds
So, we will need about 4.66 pounds of stone to cover the soil in our flower pot to a depth of about 1 1/2 inches.
For large projects you can use river stone available at lawn and garden stores. Most rounded river stones weigh about 100 pounds per cubic foot. Image © SpiderPlay, iStockphoto.
Much Larger Projects...
This same method of calculation can be applied to landscaping projects where rounded river stone is used. Since these are much larger projects we will use pounds per cubic foot for the weight of the stone. Most rounded river stones weigh about 100 pounds per cubic foot.
Let's say that we want to have a bed of shrubbery along the front of our home which is 85 feet long. And, we want that bed of shrubbery to be 5 feet wide and covered by a layer of river stone 4 inches deep. First, we calculate how many cubic feet of stone are needed by multiplying the length of the bed by its width and by the depth of the stones...
85 feet x 5 feet x 0.33 feet = 140.25 feet3
Then multiply by volume of stone needed by the density of the stone - which is 100 pounds per cubic foot.
140.25 feet3 x 100 pounds / foot3 = 14,025 pounds
You can see that we will need about 14,025 pounds of stone or a little over 7 tons.
|Hobart M. King has decades of rock tumbling experience and writes most of the articles on RockTumbler.com. He has a PhD in geology and is a GIA graduate gemologist. He also writes the articles about rocks, minerals and gems on Geology.com.|