How to Calculate Mulch
The most common mulch mistake is guessing the quantity. Too little and you make a second trip; too much and you're left with yards of material going nowhere. Here's how to get the number right the first time.
The formula
All mulch calculations come down to one formula, regardless of bed shape:
The number 324 comes from 27 cubic feet per cubic yard × 12 inches per foot. Every legitimate mulch calculator uses this same formula.
Step 1 — Measure your area
How you measure depends on the shape of the bed:
Rectangular or square beds
Example: a bed 20 ft long and 5 ft wide = 100 sq ft.
Circular beds
Example: a circular bed with a 6 ft radius = 3.14 × 36 = 113 sq ft.
Multiple or irregular beds
Break each area into rectangles or circles, calculate each one separately, then add the totals together.
Step 2 — Choose your depth
Depth affects how much material you need and how well it works. Use these standard recommendations:
| Application | Recommended depth |
|---|---|
| Flower beds, garden borders | 2–3 inches |
| Weed suppression, paths | 3–4 inches |
| Around trees (keep away from trunk) | 2–3 inches |
| Refreshing existing mulch | 1–2 inches on top |
| Playgrounds (CPSC requirement) | 6 inches minimum |
Step 3 — Calculate cubic yards
Plug your numbers into the formula. Here are worked examples:
| Area | Depth | Cubic yards |
|---|---|---|
| 100 sq ft | 2 in | 0.62 yd³ |
| 200 sq ft | 3 in | 1.85 yd³ |
| 500 sq ft | 3 in | 4.63 yd³ |
| 1,000 sq ft | 2 in | 6.17 yd³ |
| 1,000 sq ft | 3 in | 9.26 yd³ |
Step 4 — Convert to bags
If buying bagged mulch, convert cubic yards to bags:
| Bag size | Bags per cubic yard |
|---|---|
| 2 cu ft bags | 13.5 bags |
| 3 cu ft bags | 9 bags |
Always round up to the nearest whole bag. Running short mid-project means a second trip and a possible dye-lot mismatch.
Step 5 — Add waste allowance
Add 10% for flat, even beds. Add 15–20% for uneven ground, areas with mature tree roots, or beds with any grade change — mulch settles into depressions faster than expected on irregular terrain.
Skip the manual calculation
Enter your bed dimensions and depth to get cubic yards and bag count instantly.
Use the Mulch Calculator →FAQ
How do I calculate how much mulch I need?
Multiply your area in square feet by the depth in inches, then divide by 324. This gives cubic yards. For example, a 300 sq ft bed at 3 inches deep: 300 × 3 ÷ 324 = 2.78 cubic yards. Always round up.
How many bags of mulch equal a cubic yard?
1 cubic yard = 27 cubic feet. A standard 2 cu ft bag gives 13.5 bags per cubic yard. A 3 cu ft bag gives 9 bags per cubic yard.
How many square feet does a cubic yard of mulch cover?
At 1 inch deep: 324 sq ft. At 2 inches deep: 162 sq ft. At 3 inches deep: 108 sq ft. At 4 inches deep: 81 sq ft.
Should I buy bags or bulk mulch?
Buy bags for projects under 3 cubic yards — more convenient and no delivery fee. For larger projects, bulk is significantly cheaper: bagged mulch costs $47–$81 per cubic yard while bulk typically runs $30–$45 per cubic yard plus delivery.
How much extra mulch should I order?
Add 10% for flat, even beds. Add 15–20% for uneven ground, areas around tree roots, or beds with grade changes — mulch settles into depressions faster than expected.