Mulch Calculator
By Concrete Knowhow Editorial Team · Updated July 2026 · 7 min read
Quick Answer
Length
Width
Depth
Overage
Round up to cover odd-shaped beds and avoid a second trip to the store.
Common Bed Sizes: Quick Reference
| Bed Size | Depth | Cubic Yards | 2 ft³ Bags | 3 ft³ Bags |
|---|---|---|---|---|
| 10×10 ft | 2" | 0.62 | 9 | 7 |
| 10×10 ft | 3" | 0.93 | 13 | 9 |
| 10×20 ft | 2" | 1.23 | 17 | 12 |
| 10×20 ft | 3" | 1.85 | 25 | 17 |
| 20×20 ft | 3" | 3.70 | 50 | 34 |
| 20×40 ft | 3" | 7.41 | 100 | 67 |
| 50×50 ft | 2" | 15.43 | 209 | 139 |
No waste buffer included. Add 5 to 10 percent for irregular shapes.
Mulch Types Compared
The volume math is the same for every mulch, but lifespan and best use vary a lot by material. This is what actually matters when you are standing at the supply yard.
| Type | Typical Lifespan | Best For | Notes |
|---|---|---|---|
| Shredded hardwood | 1 to 2 years | General beds, slopes | Knits together, stays put on grades |
| Cedar | 2 to 3 years | Foundation beds, pathways | Natural oils slow decay and deter some insects |
| Cypress | 2 to 3 years | Wet climates | Rot resistant; check sourcing sustainability |
| Pine bark nuggets | 2 to 3 years | Flat beds, acid-loving plants | Floats and migrates in heavy rain |
| Pine straw | 6 to 12 months | Azaleas, blueberries, natural areas | Sold by the bale, not the yard |
| Dyed wood mulch | 1 to 2 years | Color-matched landscaping | Confirm the source wood; avoid near vegetable beds |
| Rubber mulch | 10+ years | Playgrounds | No soil benefit; keep away from edibles |
How the Mulch Math Works
Length times width gives square feet. Multiply by depth in feet (inches divided by 12) to get cubic feet, then divide by 27 for cubic yards. A useful shortcut: one cubic yard covers 324 square feet at 1 inch deep, so at the standard 3 inch depth, one yard covers 108 square feet.
Worked example. Three beds totaling 350 square feet at 3 inches deep: 350 times 0.25 ft equals 87.5 cubic feet, divided by 27 is 3.24 cubic yards. Round to 3.5 yards for irregular edges and you are covered.
Bulk or Bagged: Where the Break-Even Sits
One cubic yard equals 13.5 bags of 2 cubic foot mulch or 9 bags of 3 cubic foot mulch. At a typical $4 to $7 per 2 cubic foot bag, a yard of bagged mulch costs $54 to $95. Bulk mulch runs $25 to $60 per yard plus a delivery fee that is often $50 to $100 regardless of quantity. The break-even is usually around 2 to 3 cubic yards: below that, bags are competitive and easier to move; above it, bulk wins clearly. Bags also make sense when you cannot accept a driveway pile, since a yard of bulk mulch weighs 400 to 800 pounds and arrives loose.
How to Mulch a Garden Bed, Step by Step
- Weed thoroughly. Pull all weeds before mulching. Mulch suppresses future weed seeds but won't kill established weeds already in the bed.
- Edge the bed. Cut a clean edge with a spade or edging tool to define the border and keep mulch from spreading onto the lawn.
- Water the soil. If the ground is dry, water it before mulching. Mulch locks in whatever moisture is present, so start with moist soil.
- Apply a pre-emergent (optional). For beds prone to weed pressure, apply a granular pre-emergent before laying mulch, following label directions.
- Spread mulch 2–4 inches deep. Pour mulch into the bed and rake it level. Aim for a consistent 3-inch depth for most situations.
- Keep mulch away from stems and trunks. Leave a 2–3 inch gap around plant bases and tree trunks. Mulch piled against stems traps moisture and promotes rot and disease.
- Fluff the edges. Use a rake to feather the mulch at bed edges so it doesn't mound up against edging or lawn borders.
- Top up annually. Check depth each spring. Add a fresh 1–2 inch layer as needed rather than replacing the entire bed.
Frequently Asked Questions
- How much mulch do I need for a 10×20 ft bed at 3 inches deep?
- A 10×20 ft bed at 3 inches deep is 50 cubic feet, or about 1.85 cubic yards. That equals 25 bags of 2 ft³ mulch or 17 bags of 3 ft³ mulch.
- How deep should mulch be?
- Apply mulch 2–4 inches deep for most landscape beds. Shredded wood mulch at 3 inches is the most common recommendation: deep enough to suppress weeds and retain moisture, but not so deep it smothers plant roots. Keep mulch 2–3 inches away from plant stems and tree trunks.
- How many bags of mulch are in a cubic yard?
- One cubic yard equals 27 cubic feet. A 2 ft³ bag gives you 13.5 bags per cubic yard; a 3 ft³ bag gives you 9 bags per cubic yard. Bulk mulch by the yard is almost always cheaper for areas over 3 cubic yards.
- How often should I replace mulch?
- Top up mulch every 1–2 years. Organic mulches like shredded bark and wood chips decompose and enrich the soil over time. Check depth in spring, and if it has fallen below 2 inches, add a fresh layer rather than replacing everything.
- What type of mulch is best?
- Shredded hardwood bark is the most versatile. It stays in place, decomposes slowly, and looks tidy. Pine straw works well around acid-loving plants. Cedar and cypress resist insects and decompose more slowly. Avoid dyed rubber mulch near edible plants.
- Should I remove old mulch before adding new?
- Usually no. If the existing layer is still 1–2 inches deep and not matted, just loosen it with a rake and add a fresh top layer. Remove and replace only if the old mulch has become a thick, matted layer over 4–5 inches or shows signs of fungal growth.