Figuring out how much topsoil or gravel you need is a tricky business. Below I’ll take you through how our material calculator works and how much various trucks can carry.
How do I determine how much material I need?
The best way to determine how much material you need is to figure out the volume of the area you need to fill. Volume means the total space, including the length, width, and depth of the area.
Volume = Length x Width x Depth
This is the formula that our material calculator uses. It then converts the volume from cubic feet to cubic yards (27 cubic feet = 1 cubic yard).
FYI, we use the term “cubic” because the volume formula determines the dimensions of a 3D cube. We use abbreviations like yd3 and ft3 to represent the three-dimensional volume of a space in yards or feet.
You can learn from this real-life example:
A homeowner had a French drain that’s 95 feet long and 1 foot wide. It needed to be topped off with 2 inches of drain rock.
First, we needed to estimate the volume of material in cubic yards using the volume formula:
Volume = Length (95 feet) x Width (1 foot) x Depth (2 inches, which is 0.17 feet)
In other words, Volume = 95 ft x 1 ft x 0.17 ft
After multiplying the numbers, our Volume = 16.2 cubic feet (or 16.2 ft3)
Don’t forget to use the same unit of measurement, like feet or inches, for each measurement. That’s why we converted the depth from 2 inches to 0.17 feet. Forgetting to do this is when mistakes most often happen.
After getting the volume, we converted cubic feet to cubic yards by dividing our total by 27.
Volume in Cubic Yards = 16.2 ft3 ÷ 27 = 0.6 cubic yards (or 0.6 yd3)
Washington Rock will convert the volume to tonnage for you. But just to show you what this looks like, this is the formula we used this time around:
Approximate Tonnage = Cubic Yards x 1.4
In other words, Approximate Tonnage = 0.6 yd3 x 1.4
Our total came out to 0.8 tons.
We ended up using less than 1 ton of material on this project, so our calculations were right on.
Why are some materials sold by cubic yards and some sold by tons?
A cubic yard is a measure of volume while a ton is a measure of weight. The volume of the space you need to fill will always be the same, but the total weight of the materials you need will vary by the material. For example, a cubic yard of crushed rock is lighter than a cubic yard of topsoil.
The reason Washington Rock sells topsoil and sand by cubic yard rather than by ton is that their weight varies with the seasons. Topsoil and sand are heavier during the rainy season when they’re wet but lighter during the dry season. We do calculations throughout the year to figure out how much water the material has absorbed. Then our team members calculate how much of a ton of material is water weight and subtract that from the total. Buying topsoil and sand by volume means that you pay for the material rather than the water that’s in it. That’s especially important in the wet Pacific Northwest.
How much can my pickup truck or delivery truck carry?
Check out our handy guide below.
This post was originally published on May 18, 2018, and was updated on July 9, 2020. For more information about Washington Rock’s rock products, visit our Products page.