Landscaping Equations
 
We are taking a little different direction with this section of the newsletter this month. We thought it might be fun and helpful for our readers to have access to some basic formulas that we apply in landscape estimations on a regular basis. Here are a few that you might find useful:

To estimate the amount of bulk material (topsoil, gravel, compost, mulch) needed for a project, simply multiply length x width x depth and divide by 27 to determine cubic yards.

If I want to mulch a bed that is 5’ wide by 30’ long and I am mulching 2” deep, I first need to convert my 2” into a decimal that will work with my other measurements, which are in feet. To do so, I will divide the 2 by 12 (number of inches in one foot) and get .167.
 5x30x.167= 25.05, the number of cubic feet needed.

To convert to cubic yards, I will divide by 27-the number of cubic feet in a cubic yard. The answer is .927, which we can round to one cubic yard of material.

The garden that you want to add 3 inches of compost to measures 10’ wide x 25’ long. To determine how much we need, we multiply 25(length)x10(width)x.25(depth in inches divided by 12). The answer is 62.5 cubic feet, divided by 27 (number of cubic feet in a cubic yard) =2.31 round to 2 ½ cubic yards of compost. If you are dealing with a bagged product, you can eliminate the step where you converted your cubic feet into cubic yards and divide the number of cubic feet needed by the number of cubic feet in the bag.

In our mulch example, 25.05 divided by 3 (a common bagged mulch amount)=8.35, so 9 bags are needed. This also tells us that there are about 9 (3) cubic feet bags to the cubic yard, or about (5) wheelbarrows full.

A frequently asked question is: “I am coming to pick up 2 cubic yards of product, about how much does that weigh?”

Some average weights of common materials are:
Mulches= 700-800 pounds per cubic yard
Sand or gravel= about 1 ½ tons per cubic yard
Compost= 800-1,200 pounds per cubic yards
The amount of moisture can make it very variable.
 
Other fun formulas:
To determine the amount of stone needed to construct a wall:
Length x height (face feet) x depth (the measurement from the face of the wall to the back side of the wall) = cubic feet of stone. Multiply by 160 (an average weight of 1 c.f. of stone) to determine pounds-divide by 2,000 for tons. Expect to get 20-30 face feet of wall per ton of stone and 80-90 square feet of patio per ton of flagstone.
 
For grass seed, multiply length x width of the area to be seeded to get square feet. Divide by 1,000 and multiply this number by seven. This is the amount in pounds of seed required at a rate of 7 pounds per 1,000 square feet. Compute the straw needed at a rate of 1-2 bales per 1,000 square feet.
 
To find out how many gallons of water it will take to fill your new water garden, multiply length x width x depth to get cubic feet and multiply this number by 7.48 to determine gallons of water. Is the pond is in the shape of a circle? To determine surface square feet, multiply the diameter by itself x .078 x depth to get cubic feet.
 
The amount of rainfall collected on a surface in a 1” rainfall event is equal to length x width x .61. A 2,000 square foot roof can deliver over 1,200 gallons to your rain barrels in a 1” rain.
 
To achieve positive drainage, allow 1” of fall for every 8’-10’ of slope.     
 
To find the circumference of a circle, multiply the diameter by 3.14. This is helpful in determining how many linear feet of edging that you will need to border circular shaped beds.
 
To find out how much pine straw mulch you will need, divide the total square footage by 25 to determine the number of bales needed at a 6” depth or by 50 for the number needed at a 3” depth (touch-up mulching).
 
To square a raised garden bed, measure 3’ on the width and make a mark. Measure 4’ on the length and make another mark. Move one side or the other out until the measurement between the marks is 5’. This will work with any multiple of 3-4-5 such as 6-8-10. To double-check the square, the measurement of the diagonals should be equal.
 
 There are many more practical formulas that are used daily in the field of landscape design and estimation. The most useful tool of all is experience. When you have performed a task many times, you can quickly estimate the amount of material needed.