Mulch does more than make a bed look finished. It holds moisture in the soil, blocks sunlight that would otherwise germinate weed seeds, insulates plant roots from summer heat and winter cold, and breaks down over time to feed organic matter into the ground. The frustrating part is buying it: take home too little and you make a second trip to the nursery on a weekend you had planned for planting; buy too much and you are left with piles rotting beside the garage. This mulch calculator takes the length and width of your bed, the depth you want, and the size and price of the bags at your local store, then tells you exactly how many bags to load into the cart and roughly what it will cost.
The math itself is simple geometry. You are computing the volume of a shallow slab: the area of the bed in square feet, multiplied by the depth of the mulch layer in feet. Because depth is usually measured in inches, you divide by 12 first. Volume in cubic feet divided by the size of one bag gives the number of bags, always rounded up, because the store sells whole bags and running out mid-bed is the one mistake worth avoiding.
How to Use
- Measure the Bed Width — the shorter side of the bed — in feet. Pace it out, or measure with a tape. For curved or irregular beds, break the shape into rectangles and add the widths.
- Enter the Bed Length in feet. The calculator multiplies the two to get your bed area in square feet.
- Set the Mulch Depth in inches. A 2-inch layer is fine for aesthetics and moisture retention; 3 inches is the most common DIY choice; 3–4 inches is what landscapers use for serious weed control. Do not go deeper than 4 inches on most beds, because thick mulch can lock water out of the soil and invite rot against plant stems.
- Set the Bag Size. The overwhelming majority of retail bags hold 2 cubic feet, but some premium or bulk bags are 3 cubic feet. Check the label on the stack before you assume.
- Optionally enter the Price Per Bag. If you only want the quantity, leave this at the default; if you want a budget number, type what the store actually charges — typically $3–$6 per 2 cu ft bag.
The result card then shows your bed area, the total mulch in both cubic feet and cubic yards (useful if you compare bagged mulch against a bulk-delivery quote), the rounded-up bags needed, and the estimated total cost.
The Mulch Formula
Mulch volume is just the volume of a rectangular slab:
Cubic Feet = (Bed Width × Bed Length) × (Depth in Inches ÷ 12)
Where:
- Bed Width × Bed Length is the bed area in square feet.
- Depth ÷ 12 converts inches into feet so the units match the square footage.
A worked example on a 10 ft × 10 ft bed at 3 inches deep: the area is 100 square feet, the depth is 0.25 feet, so the volume is 100 × 0.25 = 25 cubic feet. Divide by a 2 cu ft bag and you need 12.5 bags — which rounds up to 13 bags. At $4 per bag, that is $52 for the whole bed. If you instead compare it to bulk, 25 cubic feet is about 0.93 cubic yards, so a bulk yard delivered usually covers a bit more than one of these beds.
A useful sanity rule of thumb: one cubic yard (27 cubic feet) of mulch spread 3 inches deep covers roughly 100 square feet. That is why the numbers above line up so neatly — a 100 sq ft bed at 3 inches is just about one yard.
Why Depth Matters More Than You Think
The depth you choose doubles your material. At 2 inches, that same 100 sq ft bed needs about 17 cu ft; at 3 inches it needs 25 cu ft; at 4 inches it needs 33 cu ft. Spreading 4 inches on a bed you only planned to dress up means buying almost twice as many bags as a 2-inch job. Decide the goal first: 2 inches for a tidy, moisture-retaining finish around established shrubs; 3 inches for a balanced landscape bed; 3–4 inches only where weeds are a real problem or you are insulating sensitive roots.
Bagged mulch is convenient for small beds and narrow access, but it costs more per cubic foot than bulk. As a rough comparison, a $4 two-cubic-foot bag works out to about $2 per cubic foot, while a bulk cubic yard (27 cu ft) delivered often lands around $30–$45 — closer to $1.10–$1.65 per cubic foot. Once your bed is over roughly 150–200 square feet, a bulk quote usually wins, even after tipping the driver.
Examples
Example 1 — A standard flower bed. A homeowner measures a 10 ft × 10 ft bed (100 sq ft), wants 3 inches of brown hardwood mulch, and bags are the usual 2 cu ft at $4 each. The calculator returns 25 cu ft, about 0.93 cubic yards, 13 bags, and a total of $52. Buying 12 would leave the bed half a bag short, so the engine rounds up to 13 on purpose.
Example 2 — A long foundation border. A 40 ft × 3 ft bed is 120 sq ft. At 2 inches deep that is only 20 cu ft, or 10 bags of 2 cu ft at about $40. Pushing the depth to 3 inches jumps it to 30 cu ft, 15 bags, and $60 — the extra 50% depth adds 50% to the bill, which is worth deciding before you start hauling.
Example 3 — Comparing bags vs. bulk. A large 30 ft × 20 ft bed is 600 sq ft. At 3 inches it needs 150 cu ft, or about 5.6 cubic yards. In 2 cu ft bags that is 75 bags, totaling $300 at $4 each. One bulk delivery of 6 yards at $40 per yard is $240 — and far fewer trips to the car.
FAQ
How much mulch do I need for a 100 sq ft bed?
At the recommended 3-inch depth, a 100 square foot bed needs about 25 cubic feet of mulch, which equals roughly 13 standard 2 cu ft bags (or about 0.93 cubic yards). At a 2-inch depth the same bed needs only about 17 cu ft, or 9 bags.
How many cubic feet are in a bag of mulch?
Most retail bags hold 2 cubic feet of mulch. Some premium colored or shredded bags are 3 cubic feet, and large "super bags" can hold more. Always check the printed volume on the bag, because the bag size directly changes how many you need.
How many bags of mulch are in a yard?
One cubic yard is 27 cubic feet. Divide by your bag size: 27 ÷ 2 = 13.5, so a cubic yard equals about 14 bags of 2 cu ft mulch; 27 ÷ 3 = 9 bags of 3 cu ft. Landscapers order by the yard, homeowners usually buy by the bag.
What depth should I spread mulch?
Aim for 2–3 inches for general landscape beds and moisture retention. Use 3–4 inches where weed suppression is the priority, but avoid piling more than 4 inches, and keep mulch an inch or two away from tree trunks and plant stems to prevent rot and pest damage.
Is it cheaper to buy mulch by the bag or in bulk?
For small beds, bags are convenient and avoid delivery fees, working out to roughly $2 per cubic foot at $4 a bag. For large areas over about 150–200 sq ft, bulk delivery (often $30–$45 per cubic yard, about $1.10–$1.65 per cu ft) is usually cheaper even with a delivery or tip fee.
How do I calculate mulch for an irregular or curved bed?
Break the bed into rectangles or circles, calculate the square footage of each piece, add them together, then multiply by the depth in feet. For a circle, area = π × radius². Plug the total square footage and your chosen depth into this calculator.
Disclaimer
This mulch calculator is provided for informational purposes only and does not constitute professional landscaping or horticultural advice. Estimates are based on the dimensions and depth you enter and on standard volume geometry; actual coverage varies by mulch type, moisture content, settling, and how evenly it is spread. Bag sizes and prices shown are typical and should be confirmed at your local supplier. Always order a little extra and check product labels before applying.