Mulch & Topsoil Calculator
Work out how much mulch, topsoil, compost, or garden soil blend to buy - in cubic yards for bulk delivery and in bag counts for store runs. Enter your bed dimensions and target depth; the calculator adds a small waste allowance and estimates weight so you know whether a pickup truck can handle the load. Formulas are documented below.
Bed Dimensions
Results
Bulk order quantity
– cubic yards
Weights are typical dry values - wet material weighs 30–50% more. Check your vehicle's payload before hauling topsoil.
The formula this calculator uses
Bags = Volume (ft³) ÷ bag size (2 or 3 ft³), rounded up
Mulch and soil products are sold two ways: by the bag (2 or 3 cubic feet) at garden centers, and by the cubic yard in bulk. The math is identical to any volume estimate - the useful part is the conversion between the two and knowing where the price break sits.
Worked example: three 4 × 12 ft beds at 3 in
- Area: 4 × 12 × 3 beds = 144 ft²
- Volume: 144 × (3 ÷ 12) = 36 ft³ × 1.05 waste = 37.8 ft³ = 1.4 yd³
- Bags: 37.8 ÷ 2 = 19 bags of 2 cu ft, or 13 bags of 3 cu ft
- Verdict: at ~19 bags, bulk delivery wins - one yard and a half costs less than the bags and skips 19 trips from the car
Coverage chart - one cubic yard covers:
| Depth | Coverage | Typical use |
|---|---|---|
| 1 in | 324 ft² | Annual top-up over existing mulch |
| 2 in | 162 ft² | Refresh; light weed suppression |
| 3 in | 108 ft² | Standard new bed depth |
| 4 in | 81 ft² | Maximum for beds; paths |
| 6 in | 54 ft² | Topsoil fill, berms |
Bags vs. bulk: the break-even
Bagged mulch typically runs $3–7 per 2 cu ft bag ($40–95 per cubic yard equivalent); bulk mulch runs $25–60 per yard plus a delivery fee of $40–100. The break-even lands around 1 to 1.5 cubic yards - roughly 14–20 bags. Below that, bags win on convenience and no delivery fee. Above it, bulk is cheaper, and a single tarp-covered pile beats hauling twenty bags. Topsoil tips even harder toward bulk because bagged soil is disproportionately expensive.
Common mistakes
Guessing the depth. Depth drives the whole order - 2 in vs. 4 in doubles it. Decide from the table, not by eye.
Ignoring weight on topsoil. A yard of topsoil weighs about a ton. Ten bags of soil in a sedan trunk is axle abuse; a half-ton pickup legally hauls roughly half a yard.
Volcano mulching. Piling mulch against trunks invites rot and rodents. Keep a 2–3 in gap around stems and a flat 3-in layer elsewhere - more mulch is not better mulch.
Buying soil for a grading problem. If you're filling a low spot that collects water, fix the drainage path first - see How to Fix Standing Water in a Yard - or the new soil simply becomes wet soil.
When to call a professional
Bulk orders above 10–15 yards, topsoil for regrading against a foundation, or soil placed over utilities deserve a landscaping contractor with a skid steer - moving 10 yards by wheelbarrow is roughly 135 trips. For fill that changes drainage patterns near structures, check grading requirements first.
Frequently Asked Questions
How much mulch do I need for 100 square feet?
At the standard 3-inch depth, 100 square feet needs 25 cubic feet - about 0.93 cubic yards, or 13 bags of 2 cu ft mulch. At 2 inches, about 0.62 cubic yards or 9 bags.
How many bags of mulch are in a cubic yard?
A cubic yard is 27 cubic feet, so it equals 13.5 bags of 2 cu ft mulch or 9 bags of 3 cu ft. Above roughly 10-12 bags, bulk delivery by the yard is usually cheaper.
How deep should mulch be?
2-3 inches for most beds. Less than 2 inches won't suppress weeds; more than 4 inches can suffocate roots and hold excess moisture against stems. Keep mulch 2-3 inches away from trunks and stems.
How much does a yard of topsoil weigh?
Screened topsoil weighs roughly 2,000-2,200 lb (about a ton) per cubic yard dry, and noticeably more when wet. A standard pickup can safely haul about half a yard to one yard.
Should I remove old mulch before adding new?
Usually no - rake and fluff the old layer, then top up to your target depth. Only remove it if it's matted, moldy, or diseased. Count only the depth you're adding when calculating.