Calculating How Much Compost You Need

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Calculating how much compost you need to cover your garden is doable, even for those with less than stellar math skills (which is totally me). As recommended in a previous post, How Much Compost to Add to the Garden, most gardens only need between ½ to 2 inches of finished compost yearly. So, how do you measure how much compost you need to cover your garden? In order to figure this out, you’ll need to know the square footage of your garden and how many inches of compost you want to add.

How to Calculate Compost Coverage in 3 Steps

Step 1: Calculate Square Footage

To calculate the square footage multiply the length by the width of your garden.

Length x Width = Square Footage

Example: 20' x 40' = 800sq. feet

Step 2: Multiply Square Footage by Compost Inches

To figure out how many inches of compost to add to your garden consult the aforementioned post How Much Compost to Add to the Garden. Multiply the square footage of your garden by the number of inches you want to add.

Example: 800 sq. feet x 1" = 800

Step 3: Divide by 12

Divide the product (total) from step 2 by 12. Doing this figures out how much cubic feet of compost you’ll need to spread it an inch thick.  

Example: 800/12 = 66.67 cubic feet

How to Measure Compost in Cubic Feet

This is where it can get tricky for those of us that are mathematically challenged. Organic Gardening suggests calculating the volume of the container holding your finished compost to figure out how much cubic feet of it you have.

To make things simpler, Organic Gardening has put together a list of conversions to make calculating the cubic feet of your compost even easier.

• 1 - 5 Gallon bucket of finished compost = 1 Cubic Foot of Finished Compost

(1 Cubic Foot of finished compost covers 12 Square Feet with 1 inch of compost)

• 1 - 30 Gallon Garbage Can of finished compost = roughly 4 Cubic Feet of Finished Compost

(4 Cubic Feet of finished compost covers 48 Square Feet with 1 inch of compost)

• 1 Finished yard of compost = 27 Cubic Feet or 200 Gallons or 1080 lbs. of Finished Compost

(27 Cubic Feet of finished compost covers 324 Square Feet with 1 inch of compost)

How to Measure Volume & Turn it into Cubic Feet

Here’s the formula to measure the volume of the container holding your finished compost.

Length x Width x Depth = Volume

Next divide the volume by 27 which tells you how many cubic yards of finished compost you have.

1 Yard = 27 Square Feet

1 Cubic Yard = 27 Cubic Feet

Cubic Yard to Cubic Feet Conversion Chart

I know I alluded to my less than savvy math skills above so I had someone double check the formulas listed above before posting this. The steps above are pretty easy to follow and calculating how much compost you really need gives you a rough idea of how much compost you need to make. 

What's your best composting tip?

Additional Composting Articles

Compost: Nature’s Organic Plant Food

6 Benefits of Composting

List of Good and Bad Compost Ingredients

How to Make Cold Compost

How to Make Hot Compost

How to Tell if Compost is Finished

How Much Compost to Add to the Garden

Calculating How Much Compost You Need

Reference: Organic Gardening (2007). Make Compost in 14 Days. Rodale Inc

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