How Much Mulch Do You Actually Need? A Border-by-Border Method
2 min read · Last reviewed March 2026
Mulch is sold by volume but bought by guesswork. Here is the arithmetic that stops you making two trips to the yard.
Mulch calculations go wrong for one of two reasons: the depth is wrong, or the area is measured in the wrong shape. Fix both and a single trip to the garden centre covers the whole bed.
Work out area, not perimeter
Rectangular beds are length times width. Circular beds are the radius squared times 3.14. Irregular borders are best split into two or three rough rectangles and added together — precision to the nearest square foot is wasted effort here.
Depth depends on the material, not habit
| Mulch type | Ideal depth | Notes |
|---|---|---|
| Shredded bark | 2-3 in | Settles about 20% in the first season |
| Wood chips | 3-4 in | Coarser texture needs more depth to block light to weeds |
| Compost | 1-2 in | Deeper smothers shallow-rooted perennials |
| Straw | 3-4 in | Very light; compresses fast in rain |
| Gravel or stone | 2 in over landscape fabric | Fabric does the weed-blocking, not depth |
Convert area and depth into volume
One cubic yard covers 100 square feet at 3 inches deep, or 162 square feet at 2 inches. Bagged mulch is typically sold in 2 cubic foot units — 13.5 bags make a cubic yard, so bulk delivery is almost always cheaper past about 8-10 bags' worth of area.
Buy bulk once you pass roughly one cubic yard
Bulk mulch delivered loose is usually 30-50% cheaper per cubic yard than bagged, but it needs a place to tip it and a wheelbarrow to move it. For small beds under 100 square feet, bagged is more convenient and the price gap is small in absolute terms.
Do I need to remove old mulch first?
No, unless it has matted into an impermeable layer or is visibly rotting and sour-smelling. Top up over sound old mulch rather than stripping it out each year.
How often should beds be topped up?
Once a year for bark and wood chips, since they break down slowly. Straw and compost mulches often need topping up twice in a growing season.
Run the numbers for your own project
- Mulch CalculatorHow much mulch do I need for my beds?
- Raised Bed Soil CalculatorHow much soil do I need to fill my raised bed?
Keep reading
- Starting Your First Vegetable Garden Without Wasting a SeasonMost first gardens fail for reasons that have nothing to do with a green thumb. Here are the five that matter.
- Building Soil That Actually Grows ThingsFeeding plants is a short-term fix. Feeding the soil is what makes a garden easy.
- Reviving a Tired Lawn: A Season-Long PlanA thin lawn is a symptom. Treating the symptom with more seed is why it keeps coming back.