Mulch Calculator
Work out how much mulch a bed needs in cubic yards and bags. Enter the bed size, choose a depth, and add a waste allowance to get an order quantity and a cost estimate you can take to a supplier.
Bed and mulch inputs
Two to four inches is typical. Do not exceed four inches around plants.
Enter the delivered bulk price, or the bag price converted to a yard equivalent.
Results
How to use the mulch calculator
Measure the bed in feet. For a rectangle, multiply length by width. For a circle, measure the widest diameter and the calculator squares half of it and multiplies by pi. If the bed is L-shaped or curved, split it into rectangles and circles, enter each section separately, and add the order quantities together.
Next, choose the depth. Three inches is the standard for a new bed: it suppresses weeds, holds moisture and still lets air reach the soil. Established beds that are already covered usually need only a one- or two-inch refresh. The calculator converts depth in inches to feet by dividing by 12, so the whole calculation stays in cubic feet before converting to cubic yards.
Bulk suppliers sell by the cubic yard. Bagged mulch is sold by volume, most often 2 cubic feet per bag, so a yard is 13.5 bags. The bag count shown here is based on the order quantity and rounded up, which is the number to buy if you are stacking bags rather than having a truck deliver. If your bags are 3 cubic feet, divide the order quantity by 3 instead of multiplying by 13.5.
Mulch depth guide
| Depth | Best for | Coverage per cubic yard |
|---|---|---|
| 1 in | Light refresh over existing mulch | 324 sq ft per yd |
| 2 in | Maintenance top-up on established beds | 162 sq ft per yd |
| 3 in | New beds and normal weed suppression | 108 sq ft per yd |
| 4 in | High weed pressure or coarse bark | 81 sq ft per yd |
| 5-6 in | Not recommended for most plantings | 54-65 sq ft per yd |
Worked example
A 20 ft by 10 ft bed is 200 square feet. At 3 inches deep, the volume is 200 x 3 / 12 = 50 cubic feet. Dividing by 27 gives 1.85 cubic yards. Add the 10% waste allowance and the order becomes 2.04 cubic yards, or 28 bags of 2 cubic feet. At $45 per delivered yard the material estimate is about $92.
If that same bed were circular with a 16 ft diameter, the area would be pi x 8 x 8 = 201 square feet. The volume and order quantity would be almost identical, which is a useful sanity check: a circle that fits inside a square covers about 79% of its area.
Bulk vs bagged mulch
Bulk is almost always cheaper per yard once the order is larger than two or three yards, even after delivery. It also saves the labor of cutting and disposing of plastic bags. Bags make more sense for small beds, steep or narrow access, or when you need a small quantity of a specialty color. Whichever route you choose, compare the price per cubic yard: a $6 bag of 2 cubic feet works out to $81 per yard, while bulk bark often lands between $30 and $55 per yard delivered.
Related Calculators
References
Frequently Asked Questions
- How many cubic yards of mulch do I need?
- Multiply the bed area in square feet by the depth in inches, then divide by 324. A 500 sq ft bed at 3 in deep needs 500 x 3 / 324 = 4.63 cubic yards. Always add 5-10% for settling, spillage and uneven edges before ordering.
- How many bags of mulch equal a cubic yard?
- A cubic yard is 27 cubic feet. Standard bags hold 2 cubic feet, so one cubic yard equals 13.5 bags. Suppliers that sell 3 cubic foot bags need 9 bags per yard. The calculator rounds up to whole bags so you do not come up short.
- How deep should mulch be?
- Two to three inches is enough for established beds. Use three to four inches on new beds or where weed pressure is high, and never exceed four inches around perennials, shrubs and trees. Deep mulch holds moisture against stems and can suffocate roots.
- Should I remove old mulch before adding new mulch?
- No, unless it has formed a water-repellent mat or is more than about four inches deep. Rake it to break the crust, pull it back from trunks and siding, then top up to the target depth. Once the total depth exceeds four inches, remove some old material first.
- How much does a cubic yard of mulch cover?
- One cubic yard covers 324 square feet at 1 inch deep, 162 square feet at 2 inches, 108 square feet at 3 inches and 81 square feet at 4 inches. Divide your bed area by that coverage number to estimate yards without the formula.
- Is bulk mulch cheaper than bagged mulch?
- Bulk mulch is usually about half the cost per cubic yard once you pass two or three yards, even after a delivery fee. Bags win for small touch-ups, steep access or when you need a specific color that is only sold bagged. Compare the delivered price per yard, not per bag.
- How much does mulch weigh per cubic yard?
- A cubic yard of bark mulch weighs roughly 400-800 lb depending on moisture and wood content. A yard of compost or topsoil weighs 1,000-1,400 lb, and gravel about 2,400-3,000 lb. Check the delivery truck and driveway limits before ordering several yards.
- Can I use this mulch calculator for a circular bed?
- Yes. Select the circular bed option and enter the diameter. The calculator uses area = pi x (diameter / 2)^2, then applies the same depth conversion. Split kidney-shaped or irregular beds into circles and rectangles and add the sections together.
- How do I keep mulch away from trees and siding?
- Keep mulch 3-6 inches away from tree trunks so the root flare stays visible, and at least 6 inches below siding or stucco. Pull it back from door thresholds and fence posts too. Mulch piled against wood traps moisture and invites rot and pests.
- Does mulch depth affect weed control?
- Yes. Two inches suppresses most annual weeds, and three inches is noticeably better. More than four inches does not improve control and can reduce oxygen in the soil. A pre-emergent herbicide or a layer of newspaper under the mulch can extend control.
- When is the best time to mulch?
- Late spring, after the soil has warmed and spring rains have soaked in, is ideal for most climates. Avoid mulching frozen ground or smothering newly emerging bulbs. A light autumn top-up is fine in cold climates, but keep it away from the crowns of perennials.
- How much extra mulch should I order for settling?
- Add 5% for fresh bark mulch and 10% for shredded or dyed mulch that settles more. Sloped beds, irregular edges and paths beside the bed need closer to 15%. The waste selector in the calculator applies the allowance to the order quantity automatically.