How much mulch do I need by bed size?
Updated April 26, 2026
Quick answer
Mulch by bed size, at standard 3-inch depth
| Bed size | Square feet | Cubic yards | 2 cu ft bags |
|---|---|---|---|
| 3 × 8 ft border | 24 sqft | 0.22 yd³ | 3 bags |
| 4 × 12 ft border | 48 sqft | 0.45 yd³ | 6 bags |
| 5 × 20 ft bed | 100 sqft | 0.93 yd³ | 13 bags |
| 10 × 10 ft island | 100 sqft | 0.93 yd³ | 13 bags |
| 10 × 20 ft bed | 200 sqft | 1.85 yd³ | 25 bags |
| 15 × 25 ft bed | 375 sqft | 3.5 yd³ | 47 bags |
| 20 × 30 ft area | 600 sqft | 5.6 yd³ | 75 bags |
| Whole front yard (1,000 sqft) | 1,000 sqft | 9.3 yd³ | 125 bags |
| Larger property (2,000 sqft) | 2,000 sqft | 18.5 yd³ | 250 bags |
Mulch by depth (per 100 sqft)
| Depth | Cubic yards | Bags (2 cu ft) | When to use |
|---|---|---|---|
| 1 in (refresh) | 0.31 yd³ | 4 bags | Topping off existing beds |
| 2 in | 0.62 yd³ | 8 bags | Light refresh, around perennials |
| 3 in (standard) | 0.93 yd³ | 13 bags | Established beds, weed control |
| 4 in | 1.23 yd³ | 17 bags | New beds, sun-baked sites |
Formula
Mulch math
yd³ = (sqft × depth_in / 12) / 27 bags_2cuft = ceil(yd³ × 13.5) bags_3cuft = ceil(yd³ × 9) Round bag counts up. You always want a few extra for top-off.
Worked example
Curved 4 × 15 ft bed at 3 inches
Standard front-yard bed along a walkway.
- 1. Approx area = 4 × 15 × 0.85 (curve factor)51 sqft
- 2. Volume = (51 × 3 / 12) / 270.47 yd³
- 3. Bags = 0.47 × 13.56.4 bags
- 4. Round up7 bags
→ Buy 7 bags, adds about $4 in coverage insurance.
Worked example
Circular bed around a tree (10 ft diameter)
Decorative ring 5 ft from trunk, 3 in mulch.
- 1. Area = π × 5²78.5 sqft
- 2. Volume = (78.5 × 3 / 12) / 270.73 yd³
- 3. Bags = 0.73 × 13.59.8 bags
- 4. Round up10 bags
→ 10 bags, keep a 6-inch ring around the trunk bare.
How thick should mulch be?
3 inches is the sweet spot for most established beds thick enough to suppress weeds and hold moisture, thin enough that water and air still reach the soil. 2 inches if you're topping off in spring; 4 inches only for new beds in full sun where you need maximum moisture retention.
Never pile mulch against tree trunks. "Mulch volcanoes" rot the bark and kill the tree. Pull mulch back at least 3 inches from any trunk or stem and keep the depth consistent across the bed, don't mound it up around plants.
Hardwood vs cypress vs cedar
| Type | Lasts | Notes |
|---|---|---|
| Hardwood (dyed or natural) | 1–2 yrs | Cheapest. Fine for decorative beds. |
| Cedar | 2–3 yrs | Repels insects. Lasts longer. Pricier. |
| Cypress | 2–3 yrs | Looks great. Often unsustainably harvested, check source. |
| Pine bark nuggets | 2 yrs | Slightly acidic. Good around evergreens. |
| Pine straw | 1 yr | Acidifies soil, use only around acid-loving plants. |
| Rubber mulch | 10+ yrs | Around play sets only. Doesn't feed soil. |
How much will I spend?
Bagged mulch runs $3.50–$5.50 per 2 cu ft bag at big boxes, or $30–$50 per cubic yard delivered in bulk (plus a $50–$120 delivery fee). For projects over 5 yards, bulk is usually cheaper, see the bag vs bulk cost guide.
Common mistakes (and how to avoid them)
✗ Mulching 5+ inches deep to 'do it once and skip a year.'
Fix: Mulch over 4 inches suffocates roots and creates anaerobic decomposition. Stay at 3 in and refresh annually with 1 in on top.
✗ Piling mulch against tree trunks (volcano mulching).
Fix: Mulch should never touch bark. Pull it back 3+ inches from any trunk. Volcano mulching kills trees within 5–10 years.
✗ Removing old mulch every year before adding new.
Fix: Top off with 1–2 inches each spring. Old mulch is breaking down into soil, that's the whole point. Only remove if matted, moldy, or already 4+ inches deep.
✗ Using pine straw or pine bark around alkaline-loving plants.
Fix: Pine acidifies soil. Use it around azaleas, blueberries, and rhodos. Use hardwood or cedar around clematis, lilacs, and most veggies.