Mulch Calculator
Results update as you type, there is no submit button.
Enter a bed's length, width and how deep you're mulching it, and this calculator returns cubic feet, cubic yards and the number of standard 2 ft³ bags, the size most garden centers stock bark and wood mulch in.
Depth Coverage Table
Three depths, and how far a standard bag stretches at each, read the middle column as "bags per 100 sq ft" at that depth.
| Depth | Bags per 100 sq ft | Notes |
|---|---|---|
| 2 in | 18 | Minimum depth that meaningfully suppresses weeds |
| 3 in | 12 | The most common recommended depth for beds |
| 4 in | 9 | Upper limit before moisture retention becomes a problem |
Organic vs. Inorganic Mulch
This calculator is built around organic mulch, bark, wood chips, shredded hardwood, pine straw, which is sold and measured by volume because it's light and settles over a season. Inorganic mulch, rubber chips, decorative rock, lava rock, is a different calculation entirely: it doesn't decompose, so you calculate it once and rarely revisit it, but it's typically sold by weight rather than volume, closer to the way the gravel calculator handles stone. If you're comparing the two for the same bed, run organic mulch through this page and inorganic options through the gravel or weight calculator instead, since a bag count and a per-ton price aren't directly comparable without converting one to match the other first.
Why Depth Matters More Here Than With Most Materials
Unlike soil or gravel, mulch has a real upper limit worth respecting, not just a recommended range. Two inches is roughly the minimum that actually suppresses weed germination; beyond four inches, the layer holds so much moisture against stems and root crowns that it starts to cause rot rather than prevent water loss. That narrow 2–4 inch window is why this calculator defaults its depth field to inches rather than feet, the numbers that matter here are always small, and a decimal-feet reading (0.25 ft, 0.33 ft) is harder to eyeball against a rake handle than "3 inches" is.
The same upper limit applies right up against tree trunks and shrub stems specifically, even within a bed mulched correctly at 3 inches overall, a thick ring piled directly against a trunk (sometimes called "volcano mulching") traps moisture against bark that isn't built to handle constant wet contact, inviting rot and pests regardless of how correct the depth is everywhere else in the bed. Keep the last two or three inches around any trunk clear down to bare soil.
Bark and wood mulch also settle and decompose over a season, losing perhaps an inch of depth by the following year even without erosion. A yearly top-dressing refresh, usually thinner than the original application, is the normal way to maintain depth rather than removing and replacing the full layer each time.
Worked Example: A 150 sq ft Border
150 sq ft of border, mulched 3 inches deep:
150 × 0.25 = 37.5 ft³
37.5 ÷ 2 = 19 bags (round up from 18.75)
For a border this size, most people compare that bag count against a bulk order before buying, the yards conversion calculator converts the same 37.5 ft³ figure to about 1.4 cubic yards, which is close enough to many suppliers' bulk minimum that it's worth calling for a price before loading up a cart with bags.
The price-per-cubic-foot comparison usually favors bulk once a job clears about a cubic yard, the same threshold covered in more depth on the yards calculator, below that line, hauling bags from a garden center avoids a bulk delivery's minimum-order fee and the need to shovel a dumped pile into a wheelbarrow yourself. Above it, most people find the bulk price per cubic foot, plus the convenience of having it dumped exactly where they want it, outweighs the extra bag handling. A landscaper mulching several properties a week skips this calculation entirely and orders bulk as a default, but for a single border or two, running the numbers first is worth the two minutes it takes.
Measuring Beds That Aren't Simple Rectangles
Most mulch beds are curved borders, not clean rectangles, which makes the area harder to measure directly than a patio or a driveway. The practical approach is to approximate the curved bed as a series of rectangular or triangular sections, a long curved border might become three or four straight-sided pieces laid end to end, calculate each section's area separately, and add them together before running the total through this calculator. This is the same divide-and-sum logic used for any irregular shape: overestimate slightly by rounding each section's edges outward rather than in, since running a little short on mulch mid-job is more disruptive than having a partial bag left over.
For beds that wrap around trees, shrubs or a patio corner, subtract those obstructions' footprint from the total area rather than mulching around them as an afterthought, a mature tree's root flare alone can occupy two or three square feet that would otherwise be double-counted in your area estimate.
Dyed Mulch and Fading
Colored or dyed mulch, the common black, brown and red varieties, is priced and measured exactly like natural mulch in terms of volume, so none of the calculations on this page change based on color. What does change is how often you'll be reordering: dye fades under UV exposure faster than the wood underneath decomposes, so a dyed bed often looks like it needs a refresh well before the two- to three-inch depth loss that would trigger a natural-mulch top-up. If color retention matters for the look of a bed, budget for a lighter, more frequent top-dressing rather than waiting for the full depth to visibly decline before reordering.
Buying Ahead of a Delivery Season
Mulch demand is highly seasonal, most garden centers sell the bulk of a year's volume in a few spring weeks, and bulk suppliers sometimes run short on popular colors or grades during that peak window. If your calculated volume is large enough to justify a bulk order, placing it early in the season rather than waiting until the ideal planting weekend avoids both stockouts and the price bump some suppliers apply during their busiest weeks.
Frequently Asked Questions
How deep should mulch actually be?
Two to four inches, with three inches the depth most landscapers default to, enough to suppress weeds and hold moisture without smothering the soil underneath or trapping too much moisture against plant stems. Going shallower than two inches leaves weeds room to grow through, while going past four inches starts working against the plants it protects.
Why does over-mulching hurt plants instead of helping them?
A layer thicker than about four inches holds so much moisture against stems and root crowns that it encourages rot, and it can also block oxygen from reaching the soil, more is not better past a fairly low ceiling. Pulling mulch back an inch or two from each stem's base avoids the problem without losing coverage elsewhere in the bed.
How many bags of mulch does a standard pallet hold?
Most pallets carry either 50 or 75 bags depending on the bag size (2 or 3 cubic feet), which works out to roughly 100–150 cubic feet, call ahead if you're ordering a full pallet, since exact counts vary by brand.
Do I need to remove old mulch before adding a new layer?
Not usually, a thin refresh layer on top of mostly-decomposed old mulch is standard practice. Only rake out old mulch first if the existing layer has already built up past four inches or has started matting into an impermeable crust.