Ordering mulch by guesswork can leave you with either a partially covered garden bed or more material than you need.
Fortunately, estimating the amount is simpler than it looks.
With a tape measure and one formula, you can calculate how much mulch to order in a few minutes.
The Formula That Does the Work
Multiply the square footage of your garden bed by the depth of mulch you want in inches, then divide by 324. The result is the number of cubic yards you need.
Why 324? A cubic yard is 27 cubic feet, and spread one inch deep it covers 324 square feet.
Here’s how coverage changes with depth:
- 2 inches deep: about 162 square feet per cubic yard
- 3 inches deep: about 108 square feet per cubic yard
- 4 inches deep: about 81 square feet per cubic yard
Most landscape supply yards sell mulch by the cubic yard, not the bag. Mulch N’ More, a Rhode Island landscape supply yard that mills its own mulch, prices every load that way.
Measure Your Beds First
For a square or rectangular bed, multiply the length by the width in feet. A bed 20 feet long and 10 feet wide is 200 square feet.
For a round bed, measure from the center to the edge to find the radius. Multiply the radius by itself, then by 3.14. A circular bed 6 feet across has a radius of 3 feet and covers about 28 square feet.
For irregularly shaped beds, divide the bed into rectangles and circles. Calculate each section separately, then add the results together.
How Deep Should Mulch Go
For most landscape beds, 2 to 3 inches is the sweet spot. That’s deep enough to hold moisture and limit growth while allowing water and air to reach the soil.
Going past about 4 inches can keep rain and irrigation from reaching the roots, according to University of Florida Extension.
Check what’s already there before you order. Old mulch still counts toward your depth, so a bed with an inch left may only need another inch or two.
A Worked Example
Suppose you have a 200-square-foot bed and want 3 inches of fresh mulch.
200 × 3 = 600, and 600 ÷ 324 = 1.85. You’d need just under 2 cubic yards.
If the bed still has an inch of old mulch and you only add 2 inches, the math becomes 400 ÷ 324. That’s about 1.2 cubic yards.
It’s advisable to allow a little extra for uneven ground and irregular edges so you don’t run short on the job.
Bags or Cubic Yards
Bagged mulch is usually sold in 2-cubic-foot bags. Since a cubic yard holds 27 cubic feet, one yard equals about 13.5 bags.
For the 200-square-foot bed above, applying 3 inches of mulch requires about 25 bags.
Bags can be convenient for small beds or a quick touch-up. For anything bigger, ordering by the cubic yard may be more practical and can reduce the number of bags you need to transport and handle.
Mulching Around Trees
Trees need a much lighter touch when it comes to mulch. Never pile mulch up against the trunk in a cone, a practice commonly called “volcano mulching.”
Mulch piled against bark can keep it too moist and contribute to bark damage, while creating conditions that may encourage pests and disease.
Their advice is a ring extending 2 to 3 feet out from the trunk, keeping it about 2 to 3 inches deep and off the bark. Taper the mulch down toward the surrounding lawn rather than piling it up against the tree.
A ring 3 feet out from a small tree covers about 28 square feet. At 2 inches deep, that’s a little over two bags.
A Few Tips Before You Order
Prepare your garden beds before spreading mulch by removing existing weeds. Mulch can help limit new growth, but it works best when applied to a clean bed.
Measure each bed separately, calculate the amount needed, and add the totals together to estimate your order. Taking a few minutes to measure carefully can help you avoid ordering too much or running short.
If you’re arranging delivery, plan where the mulch pile will go. Choosing a level, accessible spot close to your garden beds can make moving the material much easier.
A little planning goes a long way. Calculating how much mulch you need before ordering can save time and money, help you avoid extra trips, and ensure you have enough material to finish the job. With the right amount on hand and even application, you can give your landscape beds a neat, consistent finish.
