Mulch Calculator
Bed size and depth in — bags for the car, cubic yards for the delivery.
Keep mulch 2–3 inches clear of trunks and stems. Piling it against bark traps moisture and invites rot — the single most common mulching mistake.
How to Use the Mulch Calculator
- Measure the length and width of the bed in feet. Split curved or L-shaped beds into rectangles and add the totals.
- Tap a depth — light for a refresh over existing mulch, standard for most beds, deep for bare ground you want to keep weed-free.
- Set your bag size. Two cubic feet is the common bag, but check before you buy: the price per bag means nothing without it.
- Use the bag count for small jobs and the cubic yards figure when calling a bulk supplier.
How It's Calculated
Volume is bed area times depth. Depth is in inches, so it's divided by 12 to get feet; cubic feet are divided by 27 because a cubic yard is 3 × 3 × 3 feet.
Cubic yards = (sq ft × (depth ÷ 12)) ÷ 27
Bags = ⌈ cubic feet ÷ bag size ⌉
Worked example: a 12 ft × 6 ft bed is 72 sq ft. At 3 inches that's 72 × 0.25 = 18 cubic feet, or 0.67 yd³. In standard 2 cubic foot bags: 18 ÷ 2 = 9 bags.
Bags round up, because half a bag isn't sold. One cubic yard is 27 cubic feet, which works out to 13.5 standard bags — the number worth remembering when comparing a pallet of bags against a bulk load.
Mulch Coverage Reference
One cubic yard is 27 cubic feet. How far it spreads depends entirely on depth.
| Depth | 1 yd³ covers | 2 ft³ bags per yd³ | Typical use |
|---|---|---|---|
| 1" | 324 sq ft | 13.5 | Light top-dressing over settled mulch. |
| 2" | 162 sq ft | 13.5 | Annual refresh on an established bed. |
| 3" | 108 sq ft | 13.5 | Standard depth for most beds. |
| 4" | 81 sq ft | 13.5 | Bare ground, weed suppression, new beds. |
The bags-per-yard figure doesn't change with depth — a cubic yard is always 13.5 standard bags. Depth only changes how much ground that yard covers.
Bagged vs bulk
| Bagged | Bulk | |
|---|---|---|
| Sold as | 1.5, 2 or 3 ft³ bags | Cubic yards, loose |
| Per cubic yard | 13.5 × bag price | One yard price |
| Delivery | Carry it yourself | Flat fee, often with a minimum order |
| Best for | Under ~2 yd³, tight access, no wheelbarrow | Over ~2–3 yd³, large beds, whole-yard refresh |
| Watch for | Price per bag hides the volume — compare per ft³ | Delivery fee can wipe out the saving on small orders |
Frequently Asked Questions
Is bagged or bulk mulch cheaper?
Bulk is cheaper per cubic yard; delivery is what changes the answer. A cubic yard is about 13.5 standard 2 ft³ bags, so at typical bag prices you pay noticeably more for the same volume in bags. Delivery fees and minimum orders mean the crossover usually sits around 2–3 cubic yards. Below that, bags win on convenience and no minimum. Above it, bulk wins clearly — and you skip splitting and hauling 40 plastic sacks.
How often should mulch be replaced?
Organic mulch breaks down at roughly an inch a year, so most beds want topping up rather than replacing. Rake the old layer first to break up any crust, then add only enough to get back to depth. Strip and replace fully every three to four years, or sooner if it has matted into a water-shedding mat, smells sour, or has crept above 4 inches.
How deep should mulch be?
2–3 inches for established beds, 3–4 inches on bare ground where weed suppression is the point. Past 4 inches you starve the soil of oxygen and encourage roots to grow up into the mulch instead of down. And keep it 2–3 inches back from trunks and stems — mulch mounded against bark holds moisture where it does damage.
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