Mulch Calculator

How much mulch you need

Mulch is sold by volume, so the whole job comes down to three measurements: the area of the bed in square feet, the depth you want in inches, and the size of the bag or the price of a cubic yard.

Volume in cubic feet = area in square feet x depth in inches / 12. Divide that by 27 for cubic yards, or by the bag size for the number of bags. A 200 square foot bed at 3 inches is 200 x 0.25 = 50 cubic feet, which is 1.85 cubic yards, or 25 bags of 2 cubic feet.

Iowa State University Extension recommends 2 to 4 inches for most beds, with 2 to 3 inches around perennials, shrubs and trees. Depth is the input that moves the bill most: doubling the depth from 2 to 4 inches doubles the volume, and no amount of careful measuring fixes a depth chosen by eye.

Add a small waste allowance before you order. Five percent covers uneven spreading, spillage and the low spots at the edge of a bed, and 10 percent is safer on a slope or a bed with curves. On the 200 square foot bed, 5 percent takes 50 cubic feet to 52.5, which is 1.94 cubic yards, so you still order 2 yards but the bag count rises from 25 to 27.

Measuring beds that are not rectangles

Most front beds are rectangles or gentle curves, and a rectangle plus a rough allowance is close enough. For a circle or a triangle, the formula changes but the rest of the job does not.

Then apply the depth. The 12 foot circle at 2 inches needs 113.1 x 0.167 = 18.85 cubic feet, which is 0.70 cubic yards, so one yard covers it with a little spare, or 10 bags of 2 cubic feet. The 48 square foot triangle at 4 inches needs 48 x 0.333 = 16 cubic feet, which is 0.59 cubic yards, so 8 bags.

Two measurement habits save a return trip. Measure at the widest point rather than the average of a curve, since underordering costs a second drive. Then subtract what is not bed: a walkway, a section of lawn, the footprint of a shed. A 200 square foot bed with a 30 square foot path through it is 170 square feet of bed, which drops the order from 50 cubic feet to 42.5.

Worked example: a 200 square foot bed at 3 inches

Say the bed runs 20 feet along the house and 10 feet out, so 200 square feet, and you want a 3 inch layer.

• Area: 20 x 10 = 200 sq ft
• Depth in feet: 3 / 12 = 0.25 ft
• Volume: 200 x 0.25 = 50 cu ft
• Cubic yards: 50 / 27 = 1.85, so order 2 yards
• Bags of 2 cu ft: 50 / 2 = 25
• With 5 percent waste: 50 x 1.05 = 52.5 cu ft, which is 27 bags

Prices vary by region and season, so treat these as a shape for the comparison rather than a quote. What holds almost everywhere is the ordering: 1.85 cubic yards rounds up to 2, and a supplier will not sell 1.85 of a yard as a partial load unless the truck is already on your street.

Rounding up costs a few dollars and rounding down costs a second trip. On a 200 square foot bed the leftover from 2 yards is about 4 cubic feet, which is two bags worth, and it disappears fast around a mailbox or the base of a shrub.

Coverage per yard and per bag

Once you know the coverage of one cubic yard at a given depth, you can skip the arithmetic for common bed sizes and check a supplier's claim at the same time.

Those numbers come straight from 27 cubic feet per yard and 2 cubic feet per bag, divided by the depth in feet. A yard at 3 inches is 27 / 0.25 = 108 square feet. A 2 cubic foot bag at 3 inches is 2 / 0.25 = 8 square feet, and that small number is why a 200 square foot bed takes 25 of them.

For a bigger job, the coverage table scales without much thought. A 500 square foot bed at 3 inches needs 500 x 0.25 = 125 cubic feet, which is 4.63 cubic yards, so order 5 yards, or 63 bags. At 2 inches the same bed needs 83.3 cubic feet, 3.09 yards, so 4 yards, and 42 bags.

Check the bag before dividing. A bag labeled 2 cubic feet is twice a bag labeled 1 cubic foot, and a bag sold by quarts is a different unit again: 2 cubic feet is about 51 dry quarts. Buying 20 bags of 1.5 cubic feet gets you 30 cubic feet, not 40.

Bags or bulk: where the break-even sits

The same volume costs different amounts depending on how it arrives. A cubic yard is 13.5 bags of 2 cubic feet, so compare the price of those 13.5 bags against the price of one yard.

Per cubic yard, bulk is cheaper than bagged at almost any price you will see. The delivery fee is what changes the answer. A flat $65 delivery adds $65 to a one yard order and $13 a yard to a five yard order, so the delivered break-even in this example sits near 3.7 yards: below that, bags cost less than a delivered load, and above it the load wins.

Picking up yourself removes the delivery fee but adds a vehicle limit. A pickup bed holds roughly 1 to 1.5 cubic yards of loose mulch, so a 5 yard order becomes three or four trips. Bring a tarp, since loose mulch blows out at highway speed, and check the payload rating before you fill the bed: a cubic yard of mulch weighs roughly 400 to 800 pounds depending on moisture.

Two details decide the practical choice. Yards often set a delivery minimum of 1 or 2 yards, so a half yard order is a bag job by default. And a delivery truck needs a clear path to the drop spot: a 30 foot pile at the curb means moving it twice, which is the hidden cost that makes bags look reasonable for a small front bed.

Depth by planting, and why 4 inches is the ceiling

The quantity follows the depth, so the depth has to follow the planting. These are common starting points from extension guidance.

Mississippi State Extension gives the same 2 to 4 inch range for beds and warns against piling mulch against trunks. Four inches is the practical ceiling for most beds. Deeper than that, mulch blocks oxygen and water from reaching the soil, keeps roots wet for too long, and invites fungus. A mulch volcano piled against a trunk is the worst version of this: it holds moisture on the bark and can kill a tree over several seasons. Spread the layer flat and leave a bare ring around the trunk.

For the reasoning behind each depth, the mulch depth guide covers depth planting by planting and explains the mulch volcano problem. This page answers the buying question that comes right after it: how many cubic feet, how many bags, how many yards to order, and what it costs.

Waste, settling and the second trip

A mulch order that matches the math exactly usually comes up short. Three effects eat the difference.

Waste. Spreading by shovel throws some material onto the lawn, and the edges of a curved bed never get a uniform layer. Five percent covers a normal bed, and 10 percent is the right allowance for a slope, a bed with many curves, or a first attempt at spreading.

Settling. Loose bulk mulch is fluffy when it lands and packs down after a rain or two. A 3 inch layer spread from a fresh pile can look closer to 2.5 inches a month later, which is fine for weed control and short of what you wanted if the goal was a crisp edge.

Top-up versus fresh. An existing bed needs less than a new one. Rake the old layer to break the crust, then add 1 inch if it still looks thick and 2 inches if most of it has broken down. Replacing the full 3 inches every year wastes money and pushes the total depth past 4 inches within two seasons.

Leftover mulch keeps. Pile it somewhere out of the sun, and turn it once a month so it does not go sour and matted. A leftover pile that sat in a bag all summer can smell like ammonia, which is a sign of anaerobic decay, and it is better spread thin or composted than dumped 4 inches deep on a bed.

What changes the bill

Two orders of the same volume can differ by 50 percent, and the reasons are rarely about the mulch itself.

Bag size. Bags come in 1, 1.5, 2 and 3 cubic feet, and the biggest bag is often the cheapest per cubic foot. A 3 cubic foot bag at $6 costs $2 a cubic foot, while a 2 cubic foot bag at $4.25 costs $2.13. A cubic yard takes 9 of the big bags at $54, against 13.5 of the small ones at $57.38.

Colour and material. Dyed red or black mulch costs a dollar or two more per bag than natural hardwood, and it fades. Cedar and cypress cost more and last longer. Straw and pine straw are sold by the bale and priced by coverage rather than volume, so they do not compare directly with a cubic yard.

Delivery and access. A delivery fee of $50 to $90 is normal, and a long carry from the curb can add a labour charge. If the truck cannot reach the bed, you move the pile twice, which is the real reason some people buy bags for a job the math says should be bulk.

Season. Bagged mulch goes on sale in late spring, and bulk yards get busy in the same weeks. Buying a week before the rush often beats buying during it, and storing a pallet of bags in a garage costs nothing but space.

The calculator takes your own prices for a reason. Local bag prices swing from $3 to $5 for the same 2 cubic feet, and a bulk yard in a rural county can be half the price of one inside a city. Put in the numbers from two suppliers and the cheaper option is rarely a surprise, but the size of the gap often is.