How Much Soil Do I Need?

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Estimating soil volume is easier than it sounds. All you need is this simple formula.

When you’re ordering soil in bulk, getting the right amount is crucial. One or two bags of potting soil should be fine for a small number of flower pots,. But a new raised garden bed or a similar landscaping project will take a lot more than a few bags of Miracle Gro.

You might be wondering, “How much soil do I need?” Unlike the bulk section at the grocery store, ordering soil is not about weight. The answer is all about volume.

Measuring and Estimating Soil Volume

Soil is sold by cubit feet and yards, not pounds or ounces. Joe Raboine, director of residential hardscapes at Belgard describes one cubic yard as a 3-ft. x 3-ft. x 3-ft cube.

Most of the time, you won’t be working with a perfect cubic yard. To estimate soil volume for any area, all you need is a tape measure.

“The basic formula is simple: Length x Width x Height = Volume,” says Michael Dean, co-founder of Pool Research. Then divide the number of cubic feet by 27. So one cubic yard = 27 cubic feet = 1,728 cubic inches.

How To Estimate Soil Volume: Two Examples

Let’s start with a larger example from Raboine, for a 40-foot by 50-foot yard that requires six inches of soil. First, he says, calculate the volume at a depth of one foot. “To convert to six-inch depth, simply divide in half,” he says.

DimensionsCubic FeetCubic Yards
40 feet long x 50 feet wide x 1 foot deep2,00074
40 feet long x 50 feet wide x 6 inches deep1,00037

Here’s a smaller example: For this raised garden bed, with dimensions of 84 inches long x 36 inches wide x 28.25 inches deep, there are two ways to run the formula. Raboine first finds the number of cubic inches, then divides down to cubic yards.

DimensionsCubic InchesCubic FeetCubic Yards
84 inches long x 36 inches wide x 28.25 inches deep85,42849.41.8

Dean first converts the initial dimensions from inches to feet, then runs the formula.

DimensionsCubic FeetCubic Yards
7 feet long x 3 feet wide x 2.3 feet deep48.31.8

The numbers have been rounded to the nearest tenth.

Finally, these examples are for estimating a simple rectangle. For an L-shaped raised garden bed or other unique area, divide it into rectangles or squares and find the volume of each.

Soil Calculator Tools

If math isn’t your thing, there are even easier ways to find how much soil you need. Plenty of free soil calculators can be found online. Some soil and landscape retailers build calculators into their websites.

Dean recommends the Omni Calculator. You type in your dimensions in centimeters, inches, feet or several other units of measurement. It will also give you a cost estimate if you enter a price per unit.

Soil can settle over time, so you may need to add more after a year or two. This is where bags from the garden center again come in handy. A bag of garden soil from The Home Depot is usually between one and two cubic feet.