A mulch calculator turns your bed’s length, width and depth into the cubic yards and 2 ft³ bags you need to buy. Enter your area above and GravelGenie does the math instantly, adding 10% for settling and gaps. Most beds want 2–3 inches of mulch.
How much mulch do I need?
To work out how much mulch you need, multiply the bed area (length × width in feet) by the depth in feet, then divide by 27 for cubic yards. A 100-square-foot bed at 3 inches deep needs about 1 cubic yard, which is roughly 14 of the standard 2 cubic-foot bags once a waste allowance is added.
Mulch is bought two ways — by the bulk cubic yard or by the bag — so the calculator shows both. Bags are convenient for small beds and easy to carry; bulk is far cheaper once you need more than about half a yard. For odd-shaped beds, split them into rectangles and circles, calculate each, and add the results.
How many bags of mulch are in a cubic yard?
There are about 13.5 bags of mulch in a cubic yard. A cubic yard is 27 cubic feet and the standard mulch bag holds 2 cubic feet, so 27 ÷ 2 = 13.5 bags fill one yard. That single number decides the bulk-versus-bags question: if your project needs more than roughly 7–8 bags, a bulk yard usually costs less and saves a lot of lifting.
| Depth | 1 cubic yard covers | One 2 ft³ bag covers |
|---|---|---|
| 2 inches | ~162 sq ft | ~12 sq ft |
| 3 inches | ~108 sq ft | ~8 sq ft |
| 4 inches | ~81 sq ft | ~6 sq ft |
How deep should mulch be?
Spread mulch 2 to 3 inches deep. Two inches is enough to top up an existing bed and keep it looking fresh; three inches gives stronger weed suppression and moisture retention for a new bed. Resist the urge to go deeper — more than 3–4 inches can starve roots of oxygen, and piling mulch against stems or tree trunks (a “mulch volcano”) traps moisture and invites rot. Pull mulch back a couple of inches from trunks and crowns.
| Situation | Depth | Notes |
|---|---|---|
| Refreshing an existing bed | 2 in | Top up over old mulch |
| New bed / weed control | 3 in | Over soil or fabric |
| Around trees & shrubs | 2–3 in | Keep off the trunk |
| Playground / heavy paths | 3–4 in | Rubber or coarse wood |
How much does mulch cost?
Bulk mulch usually costs $30–$50 per cubic yard at the yard, before delivery, while bagged mulch runs about $3–$6 per 2 ft³ bag. Because it takes 13.5 bags to equal a yard, a yard’s worth of bags often costs $45–$80 — noticeably more than one bulk yard plus a delivery fee once you pass a couple of yards. Dyed (black, brown, red) and premium hardwood or cedar mulches sit at the higher end; plain double-ground wood is cheapest. Delivery is typically a flat fee per load, so filling the truck lowers your cost per yard.
Which type of mulch should you use?
Match the mulch to the job. Shredded hardwood knits together and stays put on slopes; bark nuggets look tidy but float in heavy rain; rubber mulch lasts for years and suits playgrounds; straw is cheap for vegetable gardens; and compost feeds the soil while it mulches. Each weighs differently, which is why the calculator lets you pick the type — the cubic yards and bags stay the same, but the weight readout adjusts. The types of mulch guide compares look, lifespan, cost and best use in detail, and how much mulch do I need walks through the full method.
How to calculate mulch for an odd-shaped bed
Real garden beds are rarely tidy rectangles, but the math still works if you break them into simple shapes. Split an L-shaped bed into two rectangles, treat a curved border as a long rectangle at its average width, and measure a round bed or tree ring as a circle (area = π × radius²). Calculate each piece on its own, then add the results for your total. The calculator above has both rectangle and circle modes, so you can run each part in turn and sum the bags. When a bed tapers or wanders, round each measurement up slightly rather than down — a little extra mulch tops up thin spots, while coming up short means another trip to the store.
Tips for buying and spreading mulch
- Lay it on weed-free soil. Pull weeds first; mulch smothers small ones but won’t stop established weeds pushing through.
- Keep 2–3 inches, no more. Deeper wastes money and can harm plants.
- Buy bulk over ~half a yard to cut cost and lifting; use bags for small touch-ups.
- Refresh, don’t rebuild. Each year, fluff the old layer and top up to 2–3 inches rather than adding a full new depth.
- Order 10% extra for settling and uneven edges — the calculator already includes it.