How Much Compost, Soil or Mulch?

Definition of Mulch and Soil Amendments

First let’s clarify the difference between the terms mulch and soil amendments.

Mulch is a covering on the surface of the soil. The best mulches are made from natural ingredients like bark chips, shredded tree trimmings, leaves, grass clippings, compost, hay or pine needles. Mulch protects the surface from getting a hard crust following a rain or sprinkler irrigation. It moderates soil temperatures and helps deter weed invasions. In time the mulch will decompose where it comes in contact with the underlying soil providing compost for the growing plant roots.

Soil amendments are worked down into the soil to improve the root zone of our plants. Compost makes the best soil amendment as it is already decomposed. Leaves, wood chips and other un-decomposed organic materials can be worked into the soil but will require time to decompose before the area can be planted, as they tend to tie up nitrogen as they begin to decompose.

Calculate What You Need

To determine how much mulch is needed for a specific area, measure the area to be covered and calculate cubic yards. The basic formula is: Total cubic yards = (Length feet * Width feet * (Depth inches / 12)) / 27

For example:

To cover an area that is 10 feet long by 10 feet wide with 3 inches of mulch:
(100 square feet) x (3 inches/12))/27 = .93 yards which you can round up to 1 yard.

If it makes it easier, you can use a shortcut. Each cubic yard has .0031 cubic inches. Round up your result to the nearest yard or half yard, depending on how you are purchasing the material.

Area to Cover
(in square feet)
x Depth of Soil or Mulch
(in inches)
x .0031

Here are some examples of approximate amount of soil or mulch needed to cover an area:

Area in Square Feet
(Length x width)
Depth Required in Inches
1 inch 3 inches 6 inches 8 inches 12 inches
50 4 cu. feet 1/2 yard 1 yard 1 1/4 yards 2 yards
100 8 cu. feet 1 yard 2 yards 2 1/2 yards 4 yards
500 1 1/2 yards 4 1/2 yards 9 1/4 yards 12 1/3 yards 18 1/2 yards
1000 3 yards 9 1/4 yards 18 1/2 yards 24 3/4 yards 37 yards

Find out How Many Bags of Soil, Mulch, or Compost You Need

If you aren’t able to purchase or haul your materials in bulk amounts, you can calculate how many bags to buy based on the total cubic yards of mulch you need. Retailers usually sell soil and mulch by the 1 or 2 cubic feet amounts, but even if they don’t, you can quickly determine how many bags to buy.

Multiply the number of yards of material you need by 27 to find the total cubic feet, then divide by the number of cubic feet in the bag.
(1 yard x 27)/ 2 cubic feet per bag = 13.5 bags (round up to 14 bags)

Here are some examples of approximate number of bags based on common bag sizes:

# Cubic Yards Needed
Bag Size
.75 Cubic Feet 1 Cubic Foot 1.25 Cubic Feet 2 cubic Feet
1/2 Yard 18 bags 14 bags 11 bags 7 bags
1 Yard 36 bags 27 bags 22 bags 14 bags
3 Yards 108 bags 81 bags 65 bags 41 bags
10 Yards 360 bags 270 bags 216 bags 135 bags

Don’t want to do the math? Most soil yards or landscaping sites have an online calculator you can use. Find them by typing “calculate cubic yards”  in your browser search box.

Additional Resources for Soils and Composting

Soils and Composting for Austin
How to Take A Soil Sample
Texas A&M AgriLife Extension Soil, Water, and Forage Testing Laboratory
Soil Survey of Travis County Texas
Don’t Bag it, Compost it!
Leaf Management Plan

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