Mulch Calculator

Related Calculators

Table of contents

• How to use
• Common mistakes
• Definitions
• Methodology
• Limitations & assumptions

Target final mulch depth: The finished thickness of mulch wanted over the soil, measured in inches.

Existing mulch depth: The average thickness already in a bed. Refresh projects subtract this depth from the target final depth.

Mulch depth to add: The missing depth needed to reach the target. It is zero if the existing layer already meets or exceeds the target.

Square foot: A measure of surface area. For a rectangular bed, multiply length in feet by width in feet.

Cubic foot: A measure of volume equal to a space 1 foot long, 1 foot wide, and 1 foot high.

Cubic yard: A bulk-material volume equal to 27 cubic feet.

Mistake: Entering length or width in inches.
Fix: Check Project and measurement method and then recalculate. Enter bed dimensions in feet. If you already know the coverage, choose a total-area method and enter square feet.

Mistake: Calculating a refresh project as if the bed has no mulch.
Fix: Check Project and measurement method and then recalculate. Choose a refresh method and enter the average remaining mulch depth in inches.

Mistake: Leaving one bed measurement blank.
Fix: Check Project and measurement method and then recalculate. Enter a value greater than 0 for every length, width, or area field, or remove the unused bed.

Mistake: Using cubic yards as though they were a bag count.
Fix: Check Project and measurement method and then recalculate. Give the cubic-yard result to a bulk supplier. For bags, enter the cubic-foot volume of one bag from its label.

Mistake: Entering the number of bags you want in the bag-size field.
Fix: Check Project and measurement method and then recalculate. Enter the volume of one bag in cubic feet, such as 2, then use the calculated whole-bag count.

• The estimate covers mulch volume only. It does not include material price, tax, delivery fees, supplier minimums, or labor.
• Length-and-width entry treats each bed as a rectangle. For curved or irregular beds, measure or estimate the total area in square feet first.
• Refresh mode uses one average existing depth for all entered beds. If depths vary, measure several spots and use a representative average.
• The result is loose material volume before spreading, settling, or product-specific compaction. Confirm how the supplier measures and sells its mulch.
• Whole bags are rounded up and appear only when a positive bag volume in cubic feet is entered.

Calculation method

The calculator adds the area of all landscape beds. In length-and-width modes, each rectangular bed area is length times width. In total-area modes, it adds the square-foot values entered for each bed.

combined area (sq ft) = add each length (ft) x width (ft)

For a new bed, the depth to add is the target final depth. For a refresh bed, the calculator subtracts the existing mulch depth. If the existing layer is as deep as or deeper than the target, the depth to add is zero.

depth to add (in) = max(0, target final depth - existing mulch depth)

It changes inches of depth into feet, multiplies that depth by the combined area, and divides by 27 to convert cubic feet to cubic yards.

mulch to buy (cu ft) = combined area (sq ft) x depth to add (in) / 12

mulch to buy (cu yd) = mulch to buy (cu ft) / 27

If a bag size is entered, the calculator divides the cubic-foot estimate by cubic feet per bag and rounds up. Rounding up avoids a recommendation for part of a bag.

whole bags to buy = round up(mulch to buy (cu ft) / bag size (cu ft per bag))

Worked example

A 20 ft by 10 ft bed covers 200 sq ft. To refresh it from 1 inch to 3 inches, add 2 inches. The estimate is 200 x 2 / 12 = 33.33 cu ft, or 33.33 / 27 = 1.23 cu yd. With 2 cu ft bags, the calculator rounds up to 17 bags.