When you plan a garden project, you often wonder how much material you need. A common question is, “How many square feet of mulch in a yard?” The simple answer is that a “yard” when talking about mulch usually means a cubic yard, not a square yard. A cubic yard is a measure of volume. It is like a box that is 3 feet wide, 3 feet long, and 3 feet high. A square foot is a measure of area, just length times width. The number of square feet a cubic yard of mulch covers depends entirely on how deep you spread it. The deeper you spread it, the fewer square feet it will cover. For example, a cubic yard of mulch can cover about 324 square feet if spread 1 inch deep, but only 108 square feet if spread 3 inches deep. This article will help you figure out exactly how much mulch you need for your space.
Image Source: kcmulch.com
Why Mulch Matters in Your Yard
Putting mulch down is one of the best things you can do for your garden beds and landscape areas. It does many good things.
- Keeps water in: Mulch helps the soil hold onto water. This means you do not have to water as often. This is great for your plants, especially when it is hot and dry.
- Stops weeds: A layer of mulch blocks sunlight from reaching the soil surface. This makes it hard for weed seeds to sprout and grow. Fewer weeds mean less work for you.
- Makes soil better: Over time, organic mulches (like wood chips or shredded bark) break down. This adds good stuff to the soil. It helps the soil stay healthy and airy.
- Protects roots: Mulch acts like a blanket for plant roots. It keeps them cooler in the summer and warmer in the winter. This helps plants handle changes in weather better.
- Looks nice: Mulch gives your garden beds a finished, tidy look. It helps plants stand out and makes the whole area look clean.
Knowing how much mulch needed is the first step to getting these benefits without buying too much or too little.
Grasping What a ‘Yard’ of Mulch Really Means
When you buy mulch in bulk from a landscape supply place, it is almost always sold by the cubic yard. This is a measure of volume.
Cubic Yards Explained Simply
Think of a cubic yard like a giant cube. Each side of this cube is 1 yard long. Since 1 yard is the same as 3 feet, the cube is 3 feet long, 3 feet wide, and 3 feet high.
To find the volume of this cube, you multiply the length times the width times the height:
3 feet * 3 feet * 3 feet = 27 cubic feet.
So, one cubic yard of mulch is the same amount of mulch that would fill a box that is 3 feet by 3 feet by 3 feet. It contains 27 cubic feet of material. This is the base unit we will use to figure out Mulch coverage per yard.
When you buy mulch in bags from a store, the bags usually say how many cubic feet they contain (like 2 cubic feet or 3 cubic feet). We will talk more about Mulch bag coverage later. But understanding the cubic yard (27 cubic feet) is key to figuring out bulk purchases and larger areas.
Step One: Measure Your Area
Before you can figure out how much mulch you need, you must know the size of the area you want to cover. You need to find the square footage of your garden beds or other areas. This is how you Calculate mulch area.
Calculate Mulch Area: How to Find Square Feet
For simple areas like squares or rectangles, finding the square footage is easy.
- Measure the length: Use a tape measure to find out how long the area is in feet.
- Measure the width: Use the tape measure to find out how wide the area is in feet.
- Multiply: Multiply the length by the width. The answer is the area in square feet.
- Example: If your garden bed is 10 feet long and 5 feet wide, the area is 10 feet * 5 feet = 50 square feet.
Let’s try another one.
* Example: A large area along your house is 30 feet long and 8 feet wide. The area is 30 feet * 8 feet = 240 square feet.
Write down the square footage for each area you plan to mulch. If you have several garden beds, measure each one separately and add their square footage together to get the total area.
Measuring Odd Shapes
Not all garden beds are perfect squares or rectangles. You might have round beds or beds with curvy edges. Here are simple ways to measure them:
- For circles: Measure the distance across the center of the circle (this is called the diameter). Divide that number by 2 to get the radius. To find the area, use the formula: Area = π * (radius * radius). You can use 3.14 for π (pi).
- Example: A round bed has a diameter of 10 feet. The radius is 10 / 2 = 5 feet. The area is 3.14 * (5 feet * 5 feet) = 3.14 * 25 square feet = 78.5 square feet.
- For odd or irregular shapes: The easiest way is to try and break the shape down into smaller squares, rectangles, or circles. Measure each smaller part and calculate its area. Then add the areas of all the parts together.
- Another way is to use a string or hose to outline the area. Then, measure the length and the widest part of the shape. Multiply these two numbers. This gives you a rough estimate. It might be a bit more than the real area, but it is close enough for estimating mulch.
- For long, curvy beds: You can often treat a long, curvy bed like a very long rectangle. Measure the total length of the curve along the middle of the bed. Then, measure the average width of the bed in a few spots and find the average width. Multiply the total length by the average width.
- Example: A curvy bed is 50 feet long when measured down the middle. The width varies, but seems to average about 4 feet. The estimated area is 50 feet * 4 feet = 200 square feet.
Getting the area right is the first key part of the Garden bed mulch calculation. Take your time and measure carefully.
Step Two: Choosing the Right Depth
After you know the square footage of your area, the next step is to decide how deep you want the mulch layer to be. The Depth of mulch layer makes a big difference in how much mulch you will need.
Depth of Mulch Layer: How Thick Should It Be?
The right depth depends on the type of mulch you use and what you want it to do.
Common Depths and Their Uses
- 1 inch deep: This is usually too thin for most mulches, especially coarser types like wood chips. It might be okay for very fine mulch or just for looks, but it won’t do much to stop weeds or hold water. It will also break down very quickly.
- 2 inches deep: This depth is better than 1 inch. It can help a bit with weeds and moisture, especially with finer mulches. It’s often used in beds that are already mulched every year, just to top it up.
- 3 inches deep: This is a common and often recommended depth for most types of mulch, including shredded bark and wood chips. It is thick enough to block most weeds effectively and hold moisture well. It also lasts a reasonable amount of time before needing more.
- 4 inches deep: This depth gives even better weed control and moisture retention. It can be good for new beds or areas with a lot of weed problems. However, spreading it too deep (more than 4 inches) can sometimes be bad for plants, especially smaller ones, by keeping the soil too wet or preventing air from reaching the roots. It also costs more because you need more mulch.
- More than 4 inches deep: Generally not recommended for typical garden beds. It can lead to problems like suffocating plant roots or creating a hiding place for rodents.
Most people aim for a Depth of mulch layer between 2 and 4 inches, with 3 inches being a very popular choice for new mulching.
Let’s decide on a depth for our examples. Suppose we decide to use a 3-inch depth for both the rectangular bed and the curvy bed.
- Rectangular bed: 50 square feet, 3 inches deep.
- Curvy bed: 200 square feet, 3 inches deep.
Step Three: Doing the Math to Find Volume
Now you have the area in square feet and the desired depth in inches. The next step is to figure out the volume of mulch needed in cubic feet, and then Convert square feet to cubic yards.
The formula for volume is Area * Depth. But the units must match. Area is in square feet. Depth is in inches. We need to change the depth from inches into feet.
There are 12 inches in 1 foot. So, to convert inches to feet, you divide the number of inches by 12.
- 1 inch = 1/12 feet (about 0.083 feet)
- 2 inches = 2/12 feet (about 0.167 feet)
- 3 inches = 3/12 feet (0.25 feet)
- 4 inches = 4/12 feet (about 0.333 feet)
Converting Square Feet and Depth to Cubic Feet
First, let’s find the volume needed in cubic feet.
Formula: Volume in Cubic Feet = Area in Square Feet * Depth in Feet
Using our examples:
-
Rectangular bed: Area = 50 sq ft. Depth = 3 inches.
- Convert depth to feet: 3 inches / 12 inches/foot = 0.25 feet.
- Volume in cubic feet: 50 sq ft * 0.25 feet = 12.5 cubic feet.
-
Curvy bed: Area = 200 sq ft. Depth = 3 inches.
- Convert depth to feet: 3 inches / 12 inches/foot = 0.25 feet.
- Volume in cubic feet: 200 sq ft * 0.25 feet = 50 cubic feet.
So, for the rectangular bed, you need 12.5 cubic feet of mulch. For the curvy bed, you need 50 cubic feet of mulch.
Convert Square Feet to Cubic Yards: The Final Volume Calculation
Mulch is usually sold by the cubic yard in bulk. Remember that 1 cubic yard is equal to 27 cubic feet.
To convert the volume from cubic feet to cubic yards, you divide the volume in cubic feet by 27.
Formula: Volume in Cubic Yards = Volume in Cubic Feet / 27
Using our examples again:
-
Rectangular bed: Volume in cubic feet = 12.5 cubic feet.
- Volume in cubic yards: 12.5 cubic feet / 27 cubic feet/cubic yard = 0.46 cubic yards (rounded).
-
Curvy bed: Volume in cubic feet = 50 cubic feet.
- Volume in cubic yards: 50 cubic feet / 27 cubic feet/cubic yard = 1.85 cubic yards (rounded).
If you were covering both areas, the total Cubic yards of mulch needed would be 0.46 + 1.85 = 2.31 cubic yards.
Most bulk mulch suppliers sell in whole cubic yards or sometimes half cubic yards. So, if you needed 2.31 cubic yards, you would likely round up and order 2.5 or even 3 cubic yards to be safe and cover the entire area properly. It’s always better to have a little extra than not enough.
Here is a simple way to combine the steps into one formula:
Volume in Cubic Yards = (Area in Sq Ft * Depth in Inches / 12) / 27
Let’s check our numbers with this formula:
- Rectangular bed: (50 sq ft * 3 inches / 12) / 27 = (50 * 0.25) / 27 = 12.5 / 27 = 0.46 cubic yards. Correct.
- Curvy bed: (200 sq ft * 3 inches / 12) / 27 = (200 * 0.25) / 27 = 50 / 27 = 1.85 cubic yards. Correct.
This formula helps you see the relationship between square feet, depth, and Cubic yards of mulch.
Mulch Coverage Per Yard: What to Expect
Knowing the Mulch coverage per yard is helpful for quick estimates or checking your calculations. This tells you how many square feet one cubic yard of mulch will cover at a specific depth.
We know 1 cubic yard = 27 cubic feet.
We know Depth in Feet = Depth in Inches / 12.
We know Volume = Area * Depth (in feet).
So, 27 cubic feet = Area * (Depth in Inches / 12).
To find the Area that 1 cubic yard covers (Mulch coverage per yard), we rearrange the formula:
Area = 27 cubic feet / (Depth in Inches / 12)
Area = 27 * (12 / Depth in Inches)
Area = (27 * 12) / Depth in Inches
Area = 324 / Depth in Inches
This gives us a simple way to find the square footage covered by one cubic yard at any given depth.
How Far One Cubic Yard Spreads at Different Depths
Let’s use the formula Area = 324 / Depth in Inches to create a table showing Mulch coverage per yard at common depths.
| Desired Mulch Depth (Inches) | Calculation (324 / Depth) | Square Feet Covered by 1 Cubic Yard |
|---|---|---|
| 1 inch | 324 / 1 | 324 sq ft |
| 2 inches | 324 / 2 | 162 sq ft |
| 3 inches | 324 / 3 | 108 sq ft |
| 4 inches | 324 / 4 | 81 sq ft |
| 5 inches | 324 / 5 | 64.8 sq ft |
| 6 inches | 324 / 6 | 54 sq ft |
This table is very useful. If you know your total area in square feet, you can use this table to quickly estimate the Cubic yards of mulch needed.
Let’s use the table with our examples, assuming a 3-inch depth:
-
Rectangular bed area: 50 sq ft.
- From the table, 1 cubic yard covers 108 sq ft at 3 inches deep.
- You need to cover 50 sq ft. This is less than 108 sq ft.
- Amount needed = Total Area / Coverage per Yard = 50 sq ft / 108 sq ft/cubic yard = 0.46 cubic yards. Matches our earlier calculation.
-
Curvy bed area: 200 sq ft.
- From the table, 1 cubic yard covers 108 sq ft at 3 inches deep.
- Amount needed = Total Area / Coverage per Yard = 200 sq ft / 108 sq ft/cubic yard = 1.85 cubic yards. Matches our earlier calculation.
This confirms that the table is a quick way to check your work or do rough estimates.
Using a Mulch Coverage Calculator
Doing the math yourself is good, but there are many tools online that can help. A Mulch coverage calculator is a website tool where you type in your area dimensions and desired depth. It then tells you how much mulch you need.
How Online Calculators Work
Most Mulch coverage calculator tools do the same steps we just did:
- You enter the shape of your area (rectangle, circle, etc.).
- You enter the measurements (length and width, or diameter) in feet or inches. The calculator finds the square footage.
- You enter the desired depth of the mulch in inches.
- The calculator uses formulas similar to Area * (Depth in Inches / 12) / 27 to figure out the Cubic yards of mulch needed.
- Some calculators also let you choose bag size (like 2 cubic feet) and will tell you how many Bags of mulch needed.
Using a Mulch coverage calculator can save time and help avoid math mistakes. Just search online for “mulch calculator” or “mulch coverage calculator”. Always check that the calculator is asking for measurements in the units you have (feet for length/width, inches for depth).
Mulch Bag Coverage: Buying by the Bag
Sometimes, you do not need a whole truckload of mulch. For small areas, touching up existing mulch, or if you do not have a way to handle bulk delivery, buying mulch in bags is easier. The question then becomes, “How many bags do I need?” This involves understanding Mulch bag coverage.
Mulch bags sold at garden centers or hardware stores usually state the volume of mulch inside the bag. This is typically given in cubic feet. Common bag sizes are 1.5 cubic feet, 2 cubic feet, or 3 cubic feet.
Understanding Bag Sizes
- A 1.5 cubic foot bag holds 1.5 cubic feet of mulch.
- A 2 cubic foot bag holds 2 cubic feet of mulch.
- A 3 cubic foot bag holds 3 cubic feet of mulch.
To compare the cost of bags to bulk mulch, remember that 1 cubic yard = 27 cubic feet.
- How many 2 cubic foot bags make up a cubic yard? 27 cubic feet / 2 cubic feet per bag = 13.5 bags.
- How many 3 cubic foot bags make up a cubic yard? 27 cubic feet / 3 cubic feet per bag = 9 bags.
Bulk mulch is often cheaper per cubic foot or cubic yard than bagged mulch, but bags are more convenient for small jobs.
Calculating Mulch Bag Coverage from Cubic Feet
Just like with a cubic yard, the area a bag covers depends on the depth you spread it.
Formula: Area Covered by One Bag (sq ft) = Volume of Bag (cubic feet) * 12 / Depth (inches)
Let’s figure out the Mulch bag coverage for common bag sizes at a popular depth of 3 inches.
-
For a 1.5 cubic foot bag, at 3 inches deep:
- Area = 1.5 cubic feet * 12 / 3 inches = 1.5 * 4 = 6 square feet.
- A 1.5 cubic foot bag covers about 6 sq ft at 3 inches deep.
-
For a 2 cubic foot bag, at 3 inches deep:
- Area = 2 cubic feet * 12 / 3 inches = 2 * 4 = 8 square feet.
- A 2 cubic foot bag covers about 8 sq ft at 3 inches deep.
-
For a 3 cubic foot bag, at 3 inches deep:
- Area = 3 cubic feet * 12 / 3 inches = 3 * 4 = 12 square feet.
- A 3 cubic foot bag covers about 12 sq ft at 3 inches deep.
We can make a table for Mulch bag coverage at different depths for a standard 2 cubic foot bag:
| Desired Mulch Depth (Inches) | Calculation (2 cubic feet * 12 / Depth) | Square Feet Covered by One 2 Cubic Foot Bag |
|---|---|---|
| 1 inch | 2 * 12 / 1 | 24 sq ft |
| 2 inches | 2 * 12 / 2 | 12 sq ft |
| 3 inches | 2 * 12 / 3 | 8 sq ft |
| 4 inches | 2 * 12 / 4 | 6 sq ft |
This table helps you see how many square feet you can expect each bag to cover.
Bags of Mulch Needed: From Total Volume to Bags
Once you know the total volume of mulch you need for your area (in cubic feet or cubic yards), and you know the size of the bags you want to buy, you can figure out the number of Bags of mulch needed.
First, find the total volume needed in cubic feet. We did this earlier:
Volume in Cubic Feet = Area in Sq Ft * Depth in Inches / 12
Using our examples again, with a 3-inch depth:
* Rectangular bed: 12.5 cubic feet needed.
* Curvy bed: 50 cubic feet needed.
* Total needed: 12.5 + 50 = 62.5 cubic feet.
Now, let’s say we want to buy 2 cubic foot bags. To find the Bags of mulch needed, divide the total cubic feet needed by the volume per bag.
Formula: Bags Needed = Total Volume Needed (cubic feet) / Volume per Bag (cubic feet)
- For the total area needing 62.5 cubic feet, using 2 cubic foot bags:
- Bags Needed = 62.5 cubic feet / 2 cubic feet per bag = 31.25 bags.
You cannot buy a quarter of a bag, so you must round up to the next whole bag. You would need to buy 32 bags.
Let’s try with 3 cubic foot bags for the same total area (62.5 cubic feet):
* Bags Needed = 62.5 cubic feet / 3 cubic feet per bag = 20.83 bags.
* Round up to 21 bags.
This shows how to calculate Bags of mulch needed based on your total required volume.
Garden Bed Mulch Calculation: Putting It All Together
Let’s review the steps for a typical Garden bed mulch calculation from start to finish. Suppose you have a garden bed that is 15 feet long and 6 feet wide, and you want to spread mulch 3 inches deep.
Example Calculation for a Simple Bed
-
Measure the area:
- Length = 15 feet
- Width = 6 feet
- Area = Length * Width = 15 feet * 6 feet = 90 square feet. (This is your Calculate mulch area).
-
Choose the depth:
- Desired Depth of mulch layer = 3 inches.
-
Calculate the volume in cubic feet:
- Convert depth to feet: 3 inches / 12 inches/foot = 0.25 feet.
- Volume in Cubic Feet = Area * Depth (in feet) = 90 sq ft * 0.25 feet = 22.5 cubic feet.
-
Calculate the volume in cubic yards (if buying in bulk):
- Volume in Cubic Yards = Volume in Cubic Feet / 27
- Volume in Cubic Yards = 22.5 cubic feet / 27 cubic feet/cubic yard = 0.83 cubic yards (rounded).
- If buying in bulk, you would likely order 1 cubic yard.
-
Calculate Bags of mulch needed (if buying bags):
- Suppose you want to buy 2 cubic foot bags.
- Bags Needed = Total Volume Needed (cubic feet) / Volume per Bag (cubic feet)
- Bags Needed = 22.5 cubic feet / 2 cubic feet per bag = 11.25 bags.
-
Round up: You need 12 bags.
-
Suppose you want to buy 3 cubic foot bags.
- Bags Needed = 22.5 cubic feet / 3 cubic feet per bag = 7.5 bags.
- Round up: You need 8 bags.
This complete example shows all the steps to find how much mulch needed, whether you buy in bulk or bags.
Example Calculation for Multiple Areas
Imagine you have three areas to mulch:
* Area 1: A rectangle 20 ft by 10 ft.
* Area 2: A circle with a 6 ft diameter.
* Area 3: A small rectangle 5 ft by 4 ft.
You want to mulch all areas 2 inches deep.
-
Measure each area in square feet:
- Area 1: 20 ft * 10 ft = 200 sq ft.
- Area 2 (circle): Diameter = 6 ft, Radius = 3 ft. Area = 3.14 * (3 ft * 3 ft) = 3.14 * 9 sq ft = 28.26 sq ft. Round to 28 sq ft for simplicity.
- Area 3: 5 ft * 4 ft = 20 sq ft.
-
Find the total area:
- Total Area = 200 sq ft + 28 sq ft + 20 sq ft = 248 sq ft.
-
Choose the depth:
- Desired Depth = 2 inches.
-
Calculate the volume in cubic feet:
- Convert depth to feet: 2 inches / 12 inches/foot = 0.167 feet (rounded).
- Volume in Cubic Feet = Total Area * Depth (in feet) = 248 sq ft * 0.167 feet = 41.396 cubic feet. Round to 41.4 cubic feet.
-
Calculate the volume in cubic yards (bulk):
- Volume in Cubic Yards = Volume in Cubic Feet / 27
- Volume in Cubic Yards = 41.4 cubic feet / 27 cubic feet/cubic yard = 1.53 cubic yards (rounded).
- You would likely order 1.5 or 2 cubic yards.
-
Calculate Bags of mulch needed (using 2 cubic foot bags):
- Bags Needed = Total Volume Needed (cubic feet) / Volume per Bag (cubic feet)
- Bags Needed = 41.4 cubic feet / 2 cubic feet per bag = 20.7 bags.
- Round up: You need 21 bags.
This shows how to calculate for multiple areas by simply adding up the square footage before doing the volume calculation. This is the standard Garden bed mulch calculation process for larger projects.
Tips for Ordering and Spreading Your Mulch
Once you know how much mulch needed, planning for delivery and spreading helps the job go smoothly.
Buying in Bulk vs. Bags
- Bulk: Usually cheaper per yard or per cubic foot. Delivered in a pile on your driveway or lawn. Requires shovels and wheelbarrows to move. Best for large areas (more than 1 cubic yard). You order by Cubic yards of mulch.
- Bags: More expensive per cubic foot. Easy to transport in a car or truck. No large pile to deal with. Easier to handle for small areas or touch-ups. You order by Bags of mulch needed.
Consider the size of your project, your budget, and how you plan to move the mulch when deciding.
Spreading Mulch Evenly
- Have a plan for where you will place the mulch pile if buying bulk.
- Move the mulch from the pile to the garden beds using a wheelbarrow.
- Use a rake or your hands to spread the mulch layer evenly.
- Use a small ruler or your fingers to check the depth as you go. Aim for your target Depth of mulch layer across the whole area.
- Keep mulch a few inches away from the base of trees and shrubs to prevent rot and pests. This is called creating a “mulch ring” or “mulch collar”.
Accounting for Waste and Settling
- The calculations give you the exact amount for the area and depth. However, mulch settles over time. It also compresses a bit when delivered in bulk.
- It’s wise to order a little extra, especially for bulk orders. Rounding up to the next half or whole yard is common (e.g., needing 2.31 yards, order 2.5 or 3).
- If buying bags, rounding up to the nearest bag or buying one extra bag is usually enough.
- Having a little extra mulch is always better than running out before you finish the job. You can store leftovers or use them later for touch-ups.
By following these steps, you can accurately determine how much mulch needed for your landscaping project and make sure you have the right amount to do the job well. The key is accurate measurement of your area (Calculate mulch area), choosing the right Depth of mulch layer, and using simple math or a Mulch coverage calculator to find the required Cubic yards of mulch or Bags of mulch needed.
Summarizing How Much Mulch Needed
To wrap up, let’s go over the main point. How many square feet of mulch in a yard? It depends on the depth. A “yard” of mulch means a cubic yard, which is 27 cubic feet.
To figure out your needs:
- Find the total area in square feet (Calculate mulch area).
- Decide on the mulch depth in inches (Depth of mulch layer).
- Use the formula to find Cubic yards of mulch needed:
(Total Sq Ft * Depth in Inches / 12) / 27 - Or, use the Mulch coverage per yard number: 1 cubic yard covers 324 / Depth (in inches) square feet. Divide your total square feet by this number.
- If buying bags, find the total cubic feet needed: Total Sq Ft * Depth in Inches / 12. Then divide this by the cubic feet in one bag to find Bags of mulch needed (Mulch bag coverage helps here).
Using a Mulch coverage calculator can simplify these steps. Remember to round up when buying to ensure you have enough material for your Garden bed mulch calculation.
Frequently Asked Questions About Mulch Amounts
h4: How much does a cubic yard of mulch cost?
The cost varies a lot. It depends on the type of mulch (wood, bark, colored, etc.), where you live, and the supplier. A cubic yard can range from $20 to $60 or even more. Delivery costs are often extra.
h4: How long does mulch last?
This depends on the type of mulch. Organic mulches (wood, bark, compost) break down over time. Shredded bark might last 1-2 years before needing a top-up. Coarser wood chips might last longer, maybe 2-3 years. Inorganic mulches like stone or rubber last for many years but do not improve the soil.
h4: Can I put new mulch over old mulch?
Yes, usually you can. If the old mulch layer is thin (1 inch or less) and has broken down, you can add a new layer on top. However, avoid building up the mulch too deep over the years. If the old layer is still thick, you might need to remove some or just add a thin layer (1-2 inches) to freshen it up. The total depth should ideally stay within the recommended 2-4 inches.
h4: What is the difference between a cubic yard and a square yard?
A cubic yard measures volume (length * width * height, 3D). A square yard measures area (length * width, 2D). A cubic yard is 3ft x 3ft x 3ft (27 cubic feet). A square yard is 3ft x 3ft (9 square feet). Mulch is sold by volume (cubic yards or cubic feet), not by area (square feet or square yards).
h4: Should I calculate for settling?
The standard calculations give you the volume needed to achieve the target depth right after spreading. Organic mulches will settle over time as they compact and break down. If you want to maintain a certain depth year-round, you will need to add more mulch later. The initial calculation doesn’t usually include extra for future settling, but you might round up your order slightly to account for initial compression or uneven spreading.