Mulch Calculator

How much mulch do I need?

Mulch is sold by volume, not by the bag, which is why "how many bags" is hard to answer without doing the math first.

Multiply the length and width of your bed to get square feet, multiply by the depth (in feet), and you have cubic feet. Divide by 27 to get cubic yards, the unit bulk mulch is priced and delivered in.

A 10×10 ft bed (100 sq ft) at 3 inches needs 100 × 0.25 = 25 cubic feet: about 0.93 cubic yards, or 13 bags of 2 cubic feet.

How to use the mulch calculator

The mulch calculator turns a bed size and a depth into cubic yards, cubic feet and bags. The "How we calculated this" panel shows every step, and the PDF report keeps them for your supplier.

Step 1: Measure the bed

Type the length and width in feet, or the square feet if you know them. For a curved bed, split it into rectangles, circles and triangles and add them in the square footage calculator.

Step 2: Pick the depth in the mulch calculator

Choose 2, 3, 4 or 6 inches. If the bed already has mulch, type its depth under "Mulch already in the bed" and it adds only the difference.

Step 3: Set the bag size, the extra and the prices

Pick 2 or 3 cubic feet to match your bag, add 10% extra if you want a safety margin, and type your bag price and bulk price per yard to compare the two ways to buy.

Mulch coverage by area and depth

Bag counts assume standard 2 cu ft bags, rounded up to whole bags.

How much does a cubic yard of mulch cover?

A cubic yard is 27 cubic feet, so it covers 324 square feet at 1 inch and half of that at each doubling of the depth. Inch Calculator gives the same figures: 162 square feet at 2 inches and 81 at 4 inches.

How many bags of mulch are in a cubic yard?

Most bags hold 2 cubic feet, and some hold 3, according to Inch Calculator. A yard is 27 cubic feet, so it takes 13.5 bags of 2 cubic feet or 9 bags of 3 cubic feet. You cannot buy half a bag, so round up.

How deep should mulch be?

Depth decides both the weed control and the order. Too little lets light through, and too much holds water against stems and roots. These are the depths the extension services give.

Our guide on how deep mulch should be goes through beds, tree rings, paths and playgrounds one by one.

How to measure mulch for any bed shape

Every shape gets reduced to square feet first. The calculator takes length and width, so convert round and angled beds with these formulas.

Worked example: a mulch ring around a tree

A ring 6 ft across with a 1 ft clear circle around the trunk has an area of π × (3² − 0.5²) = 27.5 sq ft. At 3 inches that is 6.9 cubic feet, or 4 bags of 2 cubic feet.

Mulch around trees and shrubs: no volcanoes

Penn State Extension warns against "mulch volcanoes," where mulch is piled against the trunk. Keep it 3 to 4 inches away from the trunk base, and spread it out to the drip line. Utah State Extension adds that a few inches of mulch-free area around woody plants prevents root collar disease and rodent damage.

Adding mulch to an existing bed

If the bed already has mulch, you only need the difference between the depth you want and the depth that is there. A bed with 1 inch left that should be 3 inches deep needs 2 inches. Clemson Extension suggests replacing organic mulch every year or every other year.

Types of mulch

Mulches are either organic or inorganic. Utah State Extension says organic mulches such as wood chips, bark and pine needles improve soil structure and fertility as they break down, but need replenishing. Inorganic mulches such as rock, gravel, lava rock and recycled glass drain well and add no nutrients.

Dyed mulch uses carbon-based black dye or iron oxide red dye, says Penn State Extension. It also warns that recycled wood from before 2003 may contain CCA preservative, so buy mulch from a source that says what wood it uses.

How much does a yard of mulch weigh?

Inch Calculator says a cubic yard of mulch weighs 400 to 800 pounds depending on the material and its moisture, and that a 2 cubic foot bag weighs about 20 pounds and a 3 cubic foot bag about 30 pounds. Wet mulch is heavier, so a pickup load of 2 yards can top 1,000 pounds.

Bags vs. bulk mulch

How much does mulch cost?

Type your own prices in the calculator. At our default prices of $4.25 a bag and $32 a cubic yard, the 100 sq ft bed at 3 inches costs about $55 in 13 bags or $30 in bulk, before delivery. Delivery fees and minimum orders can change that, so ask your supplier.

Weed barrier and landscape fabric under mulch

Mulch does the weed control by blocking light, so fabric is optional. Utah State Extension says the best weed barriers are landscape fabrics that allow air exchange and water infiltration, that plastic sheeting should be avoided, and that fabric barriers last about 5 years.

Benefits of mulch

• Moisture: Clemson Extension notes that organic mulch holds moisture in the soil.
• Temperature: it keeps soil cool in summer and warm in winter.
• Weeds: a deep enough layer blocks the light weed seeds need.
• Erosion: a layer of mulch protects bare soil from heavy rain.
• Soil: organic mulch feeds the soil as it breaks down.

Common mulch mistakes

• Piling it against the trunk. Keep mulch 3 to 4 inches off the bark.
• Going too deep. More than 4 inches can hold too much moisture against roots and stems.
• Forgetting the extra. Add about 10% and round the bags up.
• Not subtracting old mulch. A top-up needs only the missing depth.

Before you order mulch

Measure each bed, pick the depth for the plants in it, and let the mulch calculator turn it into cubic yards and bags. Compare the bag price with the bulk price, add about 10% extra, and download the PDF report to take to the garden center.

Frequently asked questions