Mulch Calculator
Work out exactly how much mulch a bed needs in cubic yards, cubic feet and bags, and how much the load will weigh, from the bed dimensions and the depth you want.
🌱 What is a Mulch Calculator?
A mulch calculator converts the dimensions of a garden bed and a target mulch depth into the volume of material you actually have to buy, expressed in the three units suppliers use: cubic feet, cubic yards and retail bags. The arithmetic itself is simple, but almost everyone gets it wrong in the same place. Bed dimensions are measured in feet while mulch depth is chosen in inches, so the depth must be divided by 12 before it is multiplied by the area. Skip that step and you will order twelve times too much mulch, which is exactly the kind of mistake that ends with a driveway buried under an unusable mountain of bark.
Gardeners use this before placing a bulk order so the delivery is neither short nor wildly excessive. Landscapers use it to price a job, since mulch is usually charged per cubic yard delivered and spread. Homeowners use it in the aisle of a garden centre to convert a target depth into a bag count they can fit in the car. Anyone hauling material themselves uses the weight estimate to check that the load will not exceed the payload rating of a trailer or a pickup bed, which matters more than people expect because a soaked cubic yard of hardwood mulch can approach 1,200 pounds.
Two ideas cause most of the confusion. The first is that mulch is sold by volume, not by area, so no supplier can answer "how much do I need" without knowing the depth you intend. The second is the relationship between depth and coverage, which is inverse rather than proportional. One cubic yard covers 324 square feet at one inch, but only 108 square feet at three inches and 81 square feet at four inches. Adding a single inch of depth to a large bed can add an entire cubic yard to the order, which is why the depth field is worth thinking about rather than guessing.
This calculator handles all of it. It reports cubic yards and cubic feet, rounds the bag count up because you cannot buy part of a bag, estimates the delivered weight from the mulch type you select, states the coverage one cubic yard gives at your chosen depth, and shows a table of the same bed at depths from one to six inches so you can see the trade-off before you commit. The chart plots coverage per cubic yard against depth, with a marker at the depth you entered.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 — Standard Foundation Bed at 3 Inches
20 ft by 10 ft bed, 3 inches of shredded hardwood, 2 cubic foot bags
Example 2 — Two Narrow Borders at 2 Inches
Two 30 ft by 4 ft borders, 2 inches of pine bark, 3 cubic foot bags
Example 3 — Large Bed at 4 Inches, Bulk Territory
50 ft by 20 ft bed, 4 inches of wood chips, 2 cubic foot bags
❓ Frequently Asked Questions
🔗 Related Calculators
How much mulch do I need for my garden bed?
Multiply bed length by width to get square feet, multiply by the depth in inches divided by 12 to get cubic feet, then divide by 27 for cubic yards. A 20 ft by 10 ft bed at 3 inches deep needs 200 x 0.25 = 50 cubic feet, which is 1.85 cubic yards.
How many square feet does a cubic yard of mulch cover?
324 square feet at 1 inch deep, because a cubic yard is 27 cubic feet and 27 x 12 = 324. Divide 324 by your depth in inches for the real answer: 162 sq ft at 2 inches, 108 sq ft at 3 inches, 81 sq ft at 4 inches.
How many bags of mulch are in a cubic yard?
It depends on bag size. A cubic yard is 27 cubic feet, so it equals 27 bags of 1 cubic foot, 18 bags of 1.5 cubic feet, 13.5 bags of 2 cubic feet, or 9 bags of 3 cubic feet. Two cubic foot bags are the most common retail size in the United States.
How deep should mulch be?
Two to four inches for most wood and bark mulches, with three inches as the standard target. Thinner than two inches lets light through and weeds germinate. Thicker than four inches can restrict oxygen to roots and keep the soil surface too wet. Fine-textured mulches such as compost should be kept nearer two inches.
Is it cheaper to buy mulch in bags or in bulk?
Bulk is almost always cheaper per cubic yard once you need more than about 8 to 10 bags, since you are not paying for plastic, handling and retail shelf space. Bags win when you need a very small amount, cannot take a bulk delivery, or want to move the mulch a little at a time.
How much does a cubic yard of mulch weigh?
Roughly 500 lb for pine bark, 600 lb for wood chips, 700 lb for cypress, 800 lb for shredded hardwood, 1,000 lb for compost, 1,500 lb for rubber mulch and about 2,600 lb for stone. Wet material can weigh 50 percent more than the dry figures, so allow margin when loading a vehicle.
Should I remove old mulch before adding new mulch?
Usually no. Organic mulch breaks down into the soil, which is a benefit, so most gardeners simply top up to the target depth each year. Remove and replace only when the existing layer has already exceeded four inches, has matted into a water-repellent crust, or shows persistent fungal problems.
How do I calculate mulch for a circular bed?
Work out the circle's area first, using 3.1416 times the radius in feet squared, then treat that number as the bed area. For a ring around a tree, subtract the area of the inner circle from the outer one. Enter the resulting area as a rectangle of equivalent size, for example area divided by 10 as the length and 10 as the width.
Does mulch really suppress weeds?
Yes, mainly by blocking light so weed seeds already in the soil never germinate. It does not stop perennial weeds pushing up through it, and it does not stop new seed landing on top and rooting into the mulch layer. A consistent 3 inch depth does most of the work.
How often does mulch need replacing?
Shredded hardwood and pine bark typically need topping up once a year as they decompose and settle. Larger wood chips can last two to three years. Inorganic mulches such as stone and rubber do not decompose, but they still need periodic cleaning of accumulated leaf litter and soil.
Why does the calculator round bags up?
Because you cannot buy a fraction of a bag, and running short mid-job means a second trip. If the exact figure is 24.3 bags, the calculator reports 25. Buying one extra bag beyond that is sensible insurance against settling and uneven bed depth.
Does mulch depth change how much I need per square foot?
Directly and proportionally. Doubling depth doubles the volume of mulch required and halves the area a cubic yard covers. That inverse relationship is what the chart on this page plots, and it is why an inch of extra depth on a large bed can add a full cubic yard to the order.