Rectangular bed: 10 ft × 4 ft, 3 in deep
The 3 inch depth becomes 0.25 ft, so the volume is 40 ft² × 0.25 ft.
40 ft² × 0.25 ft = 10 ft³ ÷ 27 = 0.37 yd³
That is 5 bags of 2 ft³.
Mulch Calculator
Free mulch calculator: find out how much mulch you need in cubic yards and bags. Pick the bed shape, enter its size and depth.
Enter Your Bed Size to Calculate Mulch
Enter your dimensions, then press Calculate.
Calculate a Rectangle Area
3D view- LLength—
- WWidth—
- DDepth—
Area = length × width · Volume = area × depth
Mulch Needed for Common Bed Sizes
For most beds the honest answer is: area times depth. A bed that is 100 square feet and mulched 3 inches deep needs just under one cubic yard (0.93 to be exact). Spread it 2 inches and you need about 0.62 of a yard; go to 4 inches and it is 1.23. The table shows how the number grows with the size of the bed.
| Bed area | 2 in deep | 3 in deep | 4 in deep |
|---|---|---|---|
| 100 sq ft | 0.62 yd³ | 0.93 yd³ | 1.23 yd³ |
| 200 sq ft | 1.23 yd³ | 1.85 yd³ | 2.47 yd³ |
| 500 sq ft | 3.09 yd³ | 4.63 yd³ | 6.17 yd³ |
| 1,000 sq ft | 6.17 yd³ | 9.26 yd³ | 12.35 yd³ |
Your bed will not be an exact round number of square feet, so use the mulch calculator above for the real thing. The longer background on bags, bulk and ordering is in our guide, how much mulch do I need.
How to Use This Mulch Calculator
Measure each bed and decide on a depth. The calculator returns cubic yards for a bulk delivery and whole bags for a trip to the garden center.
- Measure the bed. For an odd shape, split it into rectangles and circles and calculate each one.
- Choose the matching shape in the dropdown. Rectangle suits most beds, circle suits round ones, and Annulus (Ring) suits a ring around a tree.
- Enter the sizes and pick a unit for each. You can mix feet, inches, yards, mm, cm and m.
- Enter the depth you plan to spread, usually in inches.
- Press Calculate, then read the cubic yards for bulk delivery, or the bag count for the bag size you will buy. Open the optional section to change the bag size, add a waste percentage or enter a price.
Mulch Formula: Calculate Mulch Cubic Yards by Hand
If you would rather work it out on paper, the sum to calculate cubic yards of mulch has three short steps.
Cubic feet = Area (ft²) × Depth (ft)
Cubic yards = Cubic feet ÷ 27
Bags = Cubic feet ÷ Bag size (ft³), rounded up
Depth has to be in feet for this to work, so 3 inches becomes 3 ÷ 12 = 0.25 ft. Bags are rounded up because you cannot buy part of one. For the full method and a shortcut for inches, see the cubic yard calculation guide. Compost and leaf mold follow the same sum, and the cubic yard calculator handles them.
Mulch Bed Shapes and Their Formulas
Few beds are perfect rectangles. Pick the drawing that looks most like your bed, choose the same shape in the mulch calculator, and fill in the lettered measurements. Every formula ends the same way: area times depth, divided by 27. Our guide to measuring curved and round beds covers the awkward outlines.
Rectangle
Foundation beds and long borders.
Area = L × W
Volume (ft³) = Area × D ÷ 12
Cubic yards = Volume ÷ 27
L = length (ft) · W = width (ft) · D = depth (in)
Example: L = 15 ft, W = 3 ft, D = 3 in. Area = 45 ft². Volume = 45 × 3 ÷ 12 = 11.25 ft³, which is 0.42 yd³.
Circle
Round island beds in a lawn.
Area = π × (Ø ÷ 2)²
Volume (ft³) = Area × D ÷ 12
Cubic yards = Volume ÷ 27
Ø = diameter (ft) · D = depth (in)
Example: Ø = 10 ft, D = 3 in. Area = 78.54 ft². Volume = 78.54 × 3 ÷ 12 = 19.64 ft³, which is 0.73 yd³.
Annulus (Ring)
A tree ring with the trunk area left clear.
Area = π ÷ 4 × (Ø₁² − Ø₂²)
Volume (ft³) = Area × D ÷ 12
Cubic yards = Volume ÷ 27
Ø₁ = outer diameter (ft) · Ø₂ = inner diameter (ft) · D = depth (in)
Example: Ø₁ = 8 ft, Ø₂ = 1 ft, D = 3 in. Area = 49.48 ft². Volume = 49.48 × 3 ÷ 12 = 12.37 ft³, which is 0.46 yd³.
Rectangle Border
A mulch strip around a lawn or patio.
Area = (L + 2b) × (W + 2b) − L × W
Volume (ft³) = Area × D ÷ 12
Cubic yards = Volume ÷ 27
L = inner length (ft) · W = inner width (ft) · b = border width (ft) · D = depth (in)
Example: L = 30 ft, W = 20 ft, b = 2 ft, D = 2 in. Area = 216 ft². Volume = 216 × 2 ÷ 12 = 36 ft³, which is 1.33 yd³.
Triangle
Corner beds where two fences meet.
Area = ½ × B × H
Volume (ft³) = Area × D ÷ 12
Cubic yards = Volume ÷ 27
B = base (ft) · H = triangle height (ft) · D = depth (in)
Example: B = 10 ft, H = 6 ft, D = 3 in. Area = 30 ft². Volume = 30 × 3 ÷ 12 = 7.5 ft³, which is 0.28 yd³.
Trapezoid
Beds that taper along a path or fence.
Area = ½ × (B₁ + B₂) × H
Volume (ft³) = Area × D ÷ 12
Cubic yards = Volume ÷ 27
B₁ = base 1 (ft) · B₂ = base 2 (ft) · H = trapezoid height (ft) · D = depth (in)
Example: B₁ = 20 ft, B₂ = 12 ft, H = 4 ft, D = 3 in. Area = 64 ft². Volume = 64 × 3 ÷ 12 = 16 ft³, which is 0.59 yd³.
Mulch Depth: How Deep Should You Spread It?
Mulch depth is a balance between weed control and plant health. Too thin and weeds push through; too thick and water and air struggle to reach the roots. The right figure depends on the mulch, the plants and your climate.
New beds
The University of Florida’s extension service recommends a layer of 2 to 3 inches on plant beds, kept at least 2 inches away from tree trunks. Finer mulches are usually spread toward the thin end and coarse bark toward the deep end.
Topping up an existing bed
If last season's layer is still there, you often only need enough to bring it back to the right depth. Measure what is left before you buy, because you may need far less than a full layer.
Around trees and shrubs
Keep mulch from piling against trunks and stems, where it can hold moisture against the bark. Leaving a clear gap is why the Annulus (Ring) shape exists: enter the outer diameter of the ring and the diameter of the gap.
Mulch Coverage: What One Yard or Bag Covers
Coverage is volume divided by depth, so it works in reverse too. This table shows what one cubic yard and one bag cover at common depths:
| Depth | 1 cubic yard | 1 ft³ bag | 2 ft³ bag | 3 ft³ bag |
|---|---|---|---|---|
| 1 in | 324 sq ft | 12 sq ft | 24 sq ft | 36 sq ft |
| 2 in | 162 sq ft | 6 sq ft | 12 sq ft | 18 sq ft |
| 3 in | 108 sq ft | 4 sq ft | 8 sq ft | 12 sq ft |
| 4 in | 81 sq ft | 3 sq ft | 6 sq ft | 9 sq ft |
Mulch Bags vs Bulk Delivery
Garden centers sell bags and landscape suppliers sell by the yard, so it helps to translate between the two. The calculator does the conversion for you, and the table shows the math behind it.
| Bag size | Bags in 1 cubic yard | Whole bags to buy |
|---|---|---|
| 1 ft³ | 27 | 27 |
| 1.5 ft³ | 18 | 18 |
| 2 ft³ | 13.5 | 14 |
| 3 ft³ | 9 | 9 |
Stores only sell whole bags, so always round up: a yard of 2 ft³ bags works out to 13.5, which means buying 14. That count is before any allowance for spillage or uneven ground, which you can add in the waste field.
Price is the usual tiebreaker. As an example, if a 2 ft³ bag costs $4.50, the 14 bags for one yard cost $63.00. Compare that with a delivered bulk price per yard from a local supplier. Those prices are only an illustration, so use your own: the optional cost fields accept a price per bag or per cubic yard.
Mulch Calculator Examples
Round bed: 8 ft across, 3 in deep
The area of a circle is π × (diameter ÷ 2)², about 50.27 ft² here.
50.2655 ft² × 0.25 ft = 12.57 ft³ ÷ 27 = 0.47 yd³
That is 7 bags of 2 ft³ (6.28 bags before rounding up).
Border around a 12 ft × 8 ft lawn, 2 ft wide, 3 in deep
Choose Rectangle Border and enter the inner size plus the border width. The border area is (16 × 12) − (12 × 8) = 96 ft².
96 ft² × 0.25 ft = 24 ft³ ÷ 27 = 0.89 yd³
That is 12 bags of 2 ft³.
Tree ring: 6 ft across with a 1 ft gap at the trunk, 3 in deep
Choose Annulus (Ring): outer diameter 6 ft, inner diameter 1 ft. The inner circle is the clear space kept around the trunk.
27.4889 ft² × 0.25 ft = 6.87 ft³ ÷ 27 = 0.25 yd³
That is 4 bags of 2 ft³ (3.44 bags before rounding up).
Tips for an Accurate Mulch Estimate
- Measure the bed at its widest and narrowest points and use the average for curved edges.
- Check the current depth of old mulch before you add more.
- Measure curved bed edges with a garden hose laid along the edge, then straighten it against a tape.
- Add your own cushion in the waste field if the bed is uneven.
- If you only know the sides of an odd shape, the Square Feet Calculator finds the square footage to type into Known Area.
Mulch Calculator FAQ
How many bags of mulch are in a cubic yard?
A cubic yard is 27 cubic feet, so it equals 27 bags of 1 ft³, 18 bags of 1.5 ft³, 13.5 bags of 2 ft³ (buy 14), or 9 bags of 3 ft³. Check the volume printed on the bag, because sizes vary between brands.
How do I calculate mulch for a round bed?
Choose Circle, enter the diameter and the depth. The calculator uses π × (diameter ÷ 2)² for the area, multiplies by the depth in feet, and divides by 27 to get cubic yards. For a ring around a tree, choose Annulus (Ring).
Does it give a bag count as well as cubic yards?
Yes. It shows cubic yards for bulk delivery and also gives a bag count for the bag size you pick in the optional section.
Does the type of mulch change how much I need?
The volume does not change, because you are covering the same area to the same depth. The weight does: wet or dense mulch is heavier per yard than dry, fluffy mulch. Bags are sold by volume, so the bag count stays the same.
Should I order extra mulch?
Mulch settles and beds are rarely perfectly even, so many people order a little more than the exact figure. Use the optional waste field with your own percentage; it is 0% unless you set it.
Can I mix feet, inches and metric units?
Yes. Every field has its own unit: feet, inches, yards, millimeters, centimeters or meters. Everything is converted exactly before the volume is calculated.
Related Guides
- How Many Bags Are in a Cubic Yard?See how many bags of mulch, soil, sand and concrete make one cubic yard, for every common bag size, and how to turn any order into a bag count.
- How Much Mulch Do I Need?Find out how much mulch you need using your garden bed size and desired depth. Includes cubic yard and bag calculations.
- How to Calculate Cubic Yards: Complete GuideCalculate cubic yards from length, width and depth with one formula, a shortcut for inches, metric conversions, worked examples and common mistakes.
- What Is a Cubic Yard?A cubic yard is a cube 3 feet on each side, or 27 cubic feet. See how big it really is, how it converts, and why soil, gravel and concrete are sold this way.
More Calculators
- CY CalculatorCubic yards, feet and meters from any shape.
- Concrete CalculatorConcrete for slabs, footings and columns, in yards and bags.
- Gravel CalculatorGravel for paths and driveways, in cubic yards and tons.
- Topsoil CalculatorTopsoil for lawns and garden beds, in cubic yards and tons.
- Sand CalculatorSand for paver bases, sandboxes and fill, in yards and tons.
- Square Feet CalculatorArea of any shape in ft², yd², m² and acres.
Cite this page
APA style
Khan, M. A. (2026, October 19). Mulch Calculator. CY Calculator. https://cycalculator.com/mulch-calculator