Calculate mulch by square footage and depth
The amount of mulch you need depends on two things: the area you're covering and how deep you want the layer. Most landscapers spread mulch 2 to 4 inches deep—2 inches for a thin, maintenance layer and 4 inches for weed suppression and moisture retention. Start by measuring the length and width of each bed in feet, multiply them together to get square footage, then use that number with your chosen depth to find how many cubic yards to buy.
One cubic yard of mulch covers roughly 160 square feet at 2 inches deep, or 80 square feet at 4 inches deep. If your beds are an odd shape, break them into rectangles, calculate each one, and add the totals. For circular beds, measure the radius (the distance from the center to the edge), multiply it by itself, multiply that result by 3.14, then use that square footage in the depth formula.
Key Takeaways
- One cubic yard of mulch covers about 160 square feet at 2 inches deep or 80 square feet at 4 inches deep.
- Measure the length and width of each bed in feet, multiply them together, then divide by the coverage rate for your chosen depth to find cubic yards needed.
- Most mulch is sold by the cubic yard at landscape supply yards, garden centers, and online retailers, with delivery available for larger orders.
- Mulch settles and breaks down over time, so you will need to add a fresh layer every 1 to 2 years depending on the type and climate.
The formula for any bed shape
To find cubic yards, start with square footage. For a rectangular bed, measure the length in feet and the width in feet, then multiply them. A bed that is 10 feet long and 4 feet wide is 40 square feet. For a triangular bed, measure the base and height in feet, multiply them, then divide by 2. For a circular bed, measure the radius (center to edge), square it (multiply it by itself), then multiply by 3.14.
Once you have square footage, divide by the coverage rate. At 2 inches deep, divide by 160. At 3 inches deep, divide by 107. At 4 inches deep, divide by 80. The result is cubic yards. If you get a decimal—say 1.5 cubic yards—round up to the next whole number when ordering, because mulch settles slightly during delivery and spreading.
If you have multiple beds, calculate each one separately and add the totals. A 40-square-foot bed at 3 inches deep needs 0.37 cubic yards (40 ÷ 107). A 60-square-foot bed at the same depth needs 0.56 cubic yards (60 ÷ 107). Together, that is 0.93 cubic yards, which rounds up to 1 cubic yard.
Depth matters for weed control and moisture
A 2-inch layer of mulch is the minimum for a finished look and light weed suppression. It works well in established beds where you are refreshing mulch annually and where the soil underneath is already relatively weed-free. Two inches is also the right depth if you are mulching around tree trunks or shrubs where you want to avoid piling mulch against the bark.
A 3-inch layer is the middle ground—it suppresses weeds better than 2 inches and holds moisture longer without being so thick that it stays wet and promotes rot. Most homeowners find 3 inches the practical choice for flower beds and vegetable gardens. A 4-inch layer is best for new beds with bare soil, areas with heavy weed pressure, or dry climates where you want maximum moisture retention. Do not go deeper than 4 inches in most cases, because the lower layers can become compacted and airless.
Where to buy mulch and what it costs
Mulch is sold by the cubic yard at landscape supply yards, garden centers, and online retailers. Local landscape suppliers usually offer the best prices and can deliver for free or a flat fee if you order several cubic yards. Home improvement stores sell mulch in bags (typically 2 cubic feet per bag, so 13 to 14 bags equal 1 cubic yard) and by the cubic yard if you order in bulk. Online retailers like Amazon and local delivery services can bring bagged mulch to your door, though shipping costs add up quickly for heavy orders.
Prices vary by region and mulch type. Standard wood mulch is the least expensive. Colored mulch (dyed red, brown, or black) costs more but lasts longer and holds color better. Hardwood mulch breaks down more slowly than softwood. Cypress and cedar mulches are aromatic and resist insects but cost significantly more. For a rough comparison, standard wood mulch at a landscape yard typically costs less per cubic yard than bagged mulch at a garden center, but you need to factor in delivery or pickup time.
Account for settling and annual top-ups
Mulch settles as it dries and breaks down. After the first year, a 4-inch layer may compress to 2 to 3 inches. In hot, dry climates or with fine-textured mulch, settling happens faster. In cool, moist climates, mulch breaks down more slowly. Plan to add a 1 to 2-inch top-up layer every 1 to 2 years to maintain weed suppression and appearance. This is much less mulch than the initial process—for a 40-square-foot bed, you might need only 0.25 cubic yards for a 1-inch refresh instead of the original 0.75 cubic yards for 4 inches.
If you are spreading mulch over an existing layer, you do not need to remove the old mulch unless it has become compacted or moldy. straightforward spread the new mulch on top. If the old layer is more than 6 inches deep, rake it out to 2 to 3 inches before adding fresh material, because excessive depth can trap moisture and cause root rot in plants.
Mulch around trees and shrubs
Trees and shrubs need mulch, but the rules are different than for beds. Spread mulch 2 to 3 inches deep in a circle around the base, but keep it 6 inches away from the trunk. Mulch piled against bark traps moisture, promotes rot, and creates a highway for insects and rodents to reach the tree. The mulch circle should extend to the drip line (the outer edge of the canopy) if possible, or at least 3 to 4 feet out for young trees.
For a mature tree with a 20-foot canopy, the mulch circle is roughly 314 square feet (radius of 10 feet × 10 feet × 3.14). At 2 inches deep, that needs about 2 cubic yards. For a young shrub with a 4-foot spread, the circle is about 12 square feet and needs 0.15 cubic yards at 2 inches. These are large areas, so mulching under trees is one of the biggest mulch expenses in a yard.
Frequently Asked Questions
How many bags of mulch equal one cubic yard?
One cubic yard equals 27 cubic feet. Most bags hold 2 cubic feet, so you need 13 to 14 bags per cubic yard. Some bags are labeled as 3 cubic feet, which means 9 bags per yard. Check the bag label for the exact volume before buying, because bag sizes vary by brand and retailer.
Can I use less mulch if I lay down landscape fabric first?
Landscape fabric suppresses weeds but does not replace mulch depth. You can reduce mulch from 4 inches to 3 inches if you use fabric underneath, but do not go below 2 inches, because mulch also regulates soil temperature and moisture. Fabric alone will not hold mulch in place on slopes or in windy areas.
What if I have an irregular or curved bed?
Break the bed into simpler shapes. A curved bed can be divided into rectangles and triangles. Calculate each section separately, add the square footages together, then divide by your coverage rate. If the bed is very irregular, lay a grid over it on paper, count the squares that fall mostly within the bed, and multiply by the square footage of each grid square.
How much mulch do I need for a vegetable garden?
Measure the length and width of the garden bed in feet and multiply them to get square footage. For vegetables, 2 to 3 inches of mulch is standard—it suppresses weeds, holds moisture, and keeps soil cool without burying shallow roots. A 4-by-8-foot bed (32 square feet) at 3 inches deep needs about 0.3 cubic yards, or roughly 4 to 5 bags of standard mulch.
Should I remove old mulch before spreading new mulch?
No, unless the old layer is compacted, moldy, or deeper than 6 inches. straightforward rake it level and spread new mulch on top. If the old mulch is matted down or has a crust, loosen it with a rake first so water can penetrate. Removing old mulch wastes money and time—the bottom layer will break down and feed the soil.