Mulch Calculator
Convert bed area and mulch depth into cubic yards and bag counts, for mulch, compost, or topsoil.
Estimates are for planning. Confirm quantities against your measured site and product packaging before ordering, and follow local building codes.
How to measure the beds
Measure each bed separately with a tape, length times width, and write the numbers down as you go. For an irregular bed, split it into rectangles in your head: a kidney-shaped bed becomes one big rectangle plus a smaller one, and slight over-coverage is fine since mulch settles anyway. Curved borders can be approximated by measuring the average width at three or four spots along the length.
For a circular bed around a tree, measure across the widest point, halve it for the radius, and use radius times radius times 3.14. A 10 foot diameter ring is about 78 square feet.
Add all the beds together for total square footage. Then decide on depth: 3 inches for new beds or bare soil, 1 to 1.5 inches if you’re topping off last year’s layer that hasn’t fully broken down. Scratch into the existing mulch first; if there’s still 2 inches of intact material under the faded surface, you need less than you think.
The formula and what it assumes
Cubic yards equals area in square feet, times depth in inches divided by 12, divided by 27. The depth division converts inches to feet so area times depth gives cubic feet, and 27 converts cubic feet to cubic yards (a yard is 3 ft x 3 ft x 3 ft). For bags: multiply yards by 13.5 for 2 cubic foot bags, or by 9 for 3 cubic foot bags.
So 300 square feet at 3 inches is 300 x 0.25 / 27, about 2.8 cubic yards, or 38 of the 2 cubic foot bags. That number surprises people. Mulch volume adds up fast at proper depth, which is why beds mulched from “a few bags” always look thin by July.
The formula assumes a uniform depth across the whole area and doesn’t add a waste factor, since mulch spreads forgivingly and a little settling is expected. It also assumes you’re measuring the open bed area, not the footprint of shrubs and trees inside it; for densely planted beds you can knock 10 to 20 percent off the area. One more assumption hiding in the depth input: 3 inches is the sweet spot for most hardwood and bark mulches. Less than 2 inches won’t suppress weeds, and more than 4 starves roots of oxygen and sheds water instead of absorbing it.
Buying tips
Bagged mulch at the big box stores comes almost entirely in 2 cubic foot bags, normally $3 to $7 each depending on type, with dyed hardwood at the low end and cedar or pine bark nuggets higher. Spring sales routinely drop them to 4 or 5 bags for $10, and at those prices bags can compete with bulk on small jobs. The 3 cubic foot bag exists mostly for pine straw alternatives and some premium lines.
Bulk mulch from a landscape supply yard runs about $25 to $60 per cubic yard for the material, plus a $50 to $100 delivery fee that’s often flat regardless of quantity. That delivery fee is the whole break-even story: below about 1.5 yards, bags win or tie; above 2 yards, bulk wins clearly and the gap widens with every yard. If you have a pickup truck, most yards will load a scoop (usually 1 yard) right into the bed and you skip the fee entirely.
What pros do: order bulk, have it dumped on a tarp in the driveway, and move it with a wheelbarrow and a mulch fork (a pitchfork moves twice what a shovel does). They also keep mulch pulled back from every trunk and stem, 3 to 6 inches of bare clearance, because mulch piled on bark holds moisture against it and rots it. Flat donut, not volcano.
A quick depth check after spreading
Rake the mulch level, then push a finger straight down in a few random spots. You should hit soil at about 3 inches. High spots get raked toward thin ones. Water the finished bed lightly; it settles the mulch, kicks off the lock-together matting that keeps it from blowing, and shows you any spots shallow enough to see soil through.
Frequently asked questions
How deep should mulch be?
3 inches is the standard recommendation for beds and around trees. Go 2 inches for fine mulches like shredded leaves that mat down, and never pile mulch against trunks or stems. A refresh over existing mulch usually only needs 1 to 1.5 inches.
How many bags of mulch are in a cubic yard?
13.5 of the standard 2 cubic foot bags, or 9 of the 3 cubic foot bags. A cubic yard is 27 cubic feet, so just divide by the bag size.
Is bulk mulch cheaper than bags?
Almost always, once you need more than about 1.5 to 2 cubic yards. Bulk runs roughly $25 to $60 per yard at the yard, while the same yard in 2 cubic foot bags costs $45 to $90 at typical prices. Delivery fees of $50 to $100 are what keep small orders in bag territory.
What's a mulch volcano and why is it bad?
It's mulch piled in a cone against a tree trunk. The trapped moisture rots bark, invites insects and disease, and encourages roots to circle into the mulch instead of the soil. Keep mulch 3 to 6 inches back from trunks and stems, shaped like a flat donut.