Measure your beds
For a rectangular bed, measure the length and width in feet. Most beds aren't rectangles, so try one of these approaches:
- Split the bed into shapes (rectangles, triangles, circles), calculate each area and add them up.
- For a long curving border, measure its length along the middle and its average width at several points.
- For a ring around a tree, the area is 3.14 × radius². A 3 ft radius ring is about 28 ft². Subtract the small circle you leave clear around the trunk.
If you know the total area, enter it as the length and set the width to 1 ft.
How deep should mulch be?
Extension services are consistent on this. Penn State Extension recommends a 2–4 in layer of organic mulch and no more, less on poorly drained soil, and only 1–2 in for fine or double-shredded mulch, because fine material lets less oxygen through. The University of Illinois suggests 2–3 in for composted materials and 3–4 in for coarse mulches.
- Keep mulch off trunks and stems. Penn State suggests pulling it back 3–5 in from young trees and 8–10 in from mature trees so the root flare shows.
- Avoid "volcano mulching". Piling mulch against the trunk keeps the bark wet and invites decay and rodents (University of Kentucky).
- Check existing depth before adding more. If there's already 2 in of old mulch, a 1 in top-up may be all a bed needs, and raking the old layer refreshes its colour.
The calculation
Volume = length × width × (depth ÷ 12) in cubic feet. Divide by 27 for cubic yards, or by the bag size for bags. A 25 × 4 ft bed at 3 in is 100 × 0.25 = 25 ft³, which is 0.93 yd³ or 13 two-cubic-foot bags. With the default 5% waste the calculator gives 0.97 yd³ (26.3 ft³) and 14 bags.
Coverage chart
| Depth | Area covered by 1 yd³ | Area covered by one 2 ft³ bag |
|---|---|---|
| 1 in | 324 ft² | 24 ft² |
| 2 in | 162 ft² | 12 ft² |
| 3 in | 108 ft² | 8 ft² |
| 4 in | 81 ft² | 6 ft² |
| Depth | Area covered by 1 m³ | Area covered by one 50 L bag |
|---|---|---|
| 2.5 cm | 40 m² | 2 m² |
| 5 cm | 20 m² | 1 m² |
| 7.5 cm | 13.3 m² | 0.67 m² |
| 10 cm | 10 m² | 0.5 m² |
One cubic yard holds 13.5 two-cubic-foot bags, or 9 three-cubic-foot bags. Mulch is sold in 1.5, 2 and 3 ft³ bags. Check the bag, because some bags are marked in quarts or litres.
Mulch needed for common areas
| Area | At 2 in | At 3 in | 2 ft³ bags at 3 in |
|---|---|---|---|
| 50 ft² | 0.31 yd³ (8.3 ft³) | 0.46 yd³ (12.5 ft³) | 7 |
| 100 ft² | 0.62 yd³ (16.7 ft³) | 0.93 yd³ (25 ft³) | 13 |
| 200 ft² | 1.23 yd³ (33.3 ft³) | 1.85 yd³ (50 ft³) | 25 |
| 300 ft² | 1.85 yd³ (50 ft³) | 2.78 yd³ (75 ft³) | 38 |
| 500 ft² | 3.09 yd³ (83.3 ft³) | 4.63 yd³ (125 ft³) | 63 |
| 1000 ft² | 6.17 yd³ (166.7 ft³) | 9.26 yd³ (250 ft³) | 125 |
| Area | At 5 cm | At 7.5 cm | 50 L bags at 7.5 cm |
|---|---|---|---|
| 5 m² | 0.25 m³ (250 L) | 0.375 m³ (375 L) | 8 |
| 10 m² | 0.5 m³ (500 L) | 0.75 m³ (750 L) | 15 |
| 20 m² | 1 m³ (1,000 L) | 1.5 m³ | 30 |
| 30 m² | 1.5 m³ | 2.25 m³ | 45 |
| 50 m² | 2.5 m³ | 3.75 m³ | 75 |
| 100 m² | 5 m³ | 7.5 m³ | 150 |
Worked examples
Front border, 40 × 3 ft at 3 inFront border, 12.2 × 0.91 m at 7.6 cm
Length 40 ft · Width 3 ft · Depth 3 in · Waste / overage 5 % · Bag size 2 ft³Length 12.19 m · Width 0.91 m · Depth 7.6 cm · Waste / overage 5 % · Bag size 56.6 L
- Volume: 1.17 yd³ (31.5 ft³)Volume: 0.892 m³ (892 L)
- Bags (2 ft³ each): 16Bags (56.6 L each): 16
Three tree rings, 6 ft across (about 28 ft² each), at 3 inThree tree rings, 1.83 m across (about 2.6 m² each), at 7.6 cm
Length 85 ft · Width 1 ft · Depth 3 in · Waste / overage 5 % · Bag size 2 ft³Length 25.91 m · Width 0.3 m · Depth 7.6 cm · Waste / overage 5 % · Bag size 56.6 L
- Volume: 0.83 yd³ (22.3 ft³)Volume: 0.632 m³ (632 L)
- Bags (2 ft³ each): 12Bags (56.6 L each): 12
Total area 3 × 28.3 ≈ 85 ft², entered as 85 × 1 ft.Total area 3 × 28.3 ≈ 7.9 m², entered as 25.9 × 0.3 m.
Large island bed, 30 × 20 ft at 2 in, bulk deliveryLarge island bed, 9.14 × 6.1 m at 5.1 cm, bulk delivery
Length 30 ft · Width 20 ft · Depth 2 in · Waste / overage 5 % · Bag size 3 ft³Length 9.14 m · Width 6.1 m · Depth 5.1 cm · Waste / overage 5 % · Bag size 85 L
- Volume: 3.89 yd³ (105 ft³)Volume: 2.97 m³
- Bags (3 ft³ each): 35Bags (85 L each): 35
Bulk or bagged?
The calculator shows both numbers so you can price them side by side. Enter a price per bag and a bulk price per cubic yard. Bulk mulch from a landscape yard usually costs less per cubic yard than bags, but you may pay for delivery or have to haul it yourself, and you'll need somewhere to dump a pile. Bags are clean, easy to carry and stack, and good for small beds or for topping up. As a rough guide, once you need more than a couple of cubic yards (around 30 bags), bulk is worth pricing.
Choosing a mulch type
- Shredded hardwood knits together and stays put on slopes, but breaks down within a season or two.
- Bark nuggets last longer and look neat, but they float and can wash away in heavy rain.
- Pine straw is light and easy to spread. The University of Maryland suggests a 2–3 in layer.
- Shredded leaves and compost are cheap or free and improve the soil as they decompose, but need topping up more often.
- Dyed mulch keeps its colour longer. Ask your supplier what wood it's made from.
- Stone or rubber doesn't decompose or feed the soil, so it's better for paths and play areas than planting beds. For stone, use the gravel calculator, which reports tons.
Checked against
Each case below is re-run against the calculator by our automated test suite.
| Case | Our result | Checked against | Result |
|---|---|---|---|
| 1 yd³ of mulch in 2 ft³ bags | 14 | InchCalculator.com mulch calculator (bag count table) | Match |
| Round bed 10 ft across, 3 in deep, no waste: volume | 0.73 yd³ (19.6 ft³) | Hand calculation | Match |
| Case | Our result | Checked against | Result |
|---|---|---|---|
| 0.76 m³ of mulch in 56.6 L bags | 14 | InchCalculator.com mulch calculator (bag count table) | Match |
| Round bed 3.05 m across, 7.6 cm deep, no waste: volume | 0.556 m³ (556 L) | Hand calculation | Match |
Frequently asked questions
How many bags of mulch in a yard?
27 ÷ 2 = 13.5, so 14 two-cubic-foot bags. With 3 ft³ bags it's 9.
How much mulch for 100 square feet?
At 3 in deep, 25 ft³: 0.93 yd³ or 13 two-cubic-foot bags. At 2 in, 16.7 ft³ (9 bags).
How much does a yard of mulch cover?
About 108 ft² at 3 in, 162 ft² at 2 in and 81 ft² at 4 in.
How much mulch do I need to prevent weeds?
A 2–4 in layer of organic mulch suppresses most annual weeds. Going deeper can harm plant roots (Penn State Extension). Pull existing weeds first.
Should I remove old mulch before adding new?
Not usually. Check the depth, rake the old mulch to break up matted layers, and add only enough to bring the total back to 2–4 in.
Sources & assumptions
The results are planning estimates, and the cost figures only use prices you enter. Product yields, densities and coverage rates vary, so check the label or ask your supplier, and follow local codes. Figures marked "approximate" or "rule of thumb" are general practice, not exact standards.
- Penn State Extension: Mulching Landscape Trees
- University of Illinois Extension: Proper Mulching Techniques
- University of Kentucky: Mulch Myths (HO-106)
- University of Maryland Extension: Mulching Trees and Shrubs
See how we calculate and test our formulas and the changelog. Last updated 2026-10-08.
Reviewed by the MaterialWhiz Editorial Team. This estimate uses the assumptions shown in the calculator. Review the result against your supplier's product coverage and site conditions. Last reviewed: October 10, 2026. See how we calculate · Report a correction.