Mulch Calculator

Volume is area times depth: cubic feet = area (sq ft) × depth (in) ÷ 12. A 200 sq ft bed at 3 inches deep is 200 × 0.25 = 50 cubic feet, which is 50 ÷ 27 ≈ 1.85 cubic yards, or 25 of the standard 2 cu ft bags. It helps to memorize the coverage of one cubic yard, since that is the unit bulk mulch is sold in. A cubic yard covers about 162 sq ft at 2 inches, 108 sq ft at 3 inches, and 81 sq ft at 4 inches. Those three numbers answer most driveway-side questions without any arithmetic. Measuring the bed is the part that goes wrong. Landscape beds are curved, so treat them as a rough rectangle or a series of rectangles and accept the approximation — mulch is forgiving, and being a few square feet out matters far less here than it would with tile. For a long border, length times average width is close enough. One caution on the bagged figure: not every bag is 2 cubic feet. Bark, cypress and some premium products come in 3 cu ft bags, and rubber and stone mulches are sometimes sold by weight instead. A cubic yard is 13.5 of the 2 cu ft bags but only 9 of the 3 cu ft ones, which is a large difference when comparing prices on a shelf. Check the bag before doing the division.

Two to three inches is the usual target for a wood mulch. That is enough to shade the soil, hold moisture through a hot week, moderate soil temperature and block most weed seeds from germinating, without cutting the soil off from the air above it. Deeper is not a stronger version of the same thing. Past about four inches, a fine-textured mulch starts to work against you: it can shed light rain rather than let it through, it keeps the soil surface cold and wet in spring, and it deprives roots of oxygen. Piling on more year after year without checking the existing depth is how beds end up under six or eight inches of accumulated material with the plants sulking in it. Texture changes the right number. Coarse, chunky bark has large air gaps and can go a little deeper; fine, shredded material packs down tighter and should stay at the lower end. Around shallow-rooted plants, and over the crowns of perennials, less is safer. The most common mulching mistake is not depth across the bed but depth against the plant. Mulch heaped up the trunk of a tree in a cone — the practice gardeners call volcano mulching — holds moisture against bark that is not adapted to it, invites rot and pests, and encourages roots to grow up into the mulch instead of out into the soil. Pull mulch back a few inches from trunks and stems so the base of the plant is exposed. A mulch ring should look like a doughnut, not a volcano.

A cubic yard is 13.5 of the standard 2 cu ft bags. That equivalence is the whole comparison: price the yard, price thirteen and a half bags, and see which is cheaper. Bulk almost always wins on price once the quantity is meaningful, and the practical crossover is usually somewhere around half a yard — roughly seven bags — because that is where the per-yard saving starts to beat the delivery fee and the hassle of a pile in the driveway. Suppliers set minimum delivery quantities, so ask before assuming a small bulk order is possible. Bags win on convenience, and convenience is not nothing. They can be bought in the exact quantity, stored unopened until you get to the job, carried to the far corner of a yard one at a time, and used without a wheelbarrow. For a couple of beds, or a property with no vehicle access to the back garden, bags are the right answer even at a higher unit price. If you go bulk, plan the drop. Mulch is much lighter than gravel — a cubic yard of wood mulch is a few hundred pounds rather than a ton and a half, so a pickup can usually manage a yard where it could not manage a yard of stone — but the whole load still lands in one cone wherever the truck can reach, and every bit of it moves by wheelbarrow from there.

Refreshing is a different calculation from starting fresh, and treating it like a new bed is how mulch accumulates to unhealthy depths. Organic mulch decomposes, which is a feature: it is slowly becoming soil, adding organic matter and feeding soil life. That is why a bed needs topping up, usually once a year, and why the amount needed is only the difference between what is there now and the target depth. So measure first. Push a finger or a trowel down through the existing layer to the soil and see what you actually have. If two inches remain and you want three, order for one inch, not three — a third of the volume, and a third of the cost. Beds that look tired often need raking rather than more material: fluffing a matted surface layer restores the appearance and the water penetration without adding anything. If the existing mulch has matted into a crust that water runs off, break it up before adding to it. And if the bed is already at or above four inches, pull material out rather than adding, especially away from trunks and crowns. One agronomic nuance worth knowing, because it circulates as a scare: fresh wood chips do tie up nitrogen as they break down, but on the surface that effect is largely confined to the thin zone where mulch meets soil, and established shrubs and trees rooting below it are little affected. Where it genuinely matters is if you till fresh woody material into the soil, or spread it thickly over shallow-rooted annuals and seedlings. As a surface mulch around established plants, it is not the problem it is made out to be.

Wood mulches — shredded hardwood, bark, chips — are the default, and they are the ones that improve soil as they break down. Shredded material knits together and stays put on a slope better than loose chips, which is a real consideration on a bank where chips will float away in a downpour. Dyed mulches are colored wood, and the base wood may be recycled material of varying origin. If the source matters to you, ask the supplier what it is made from. Stone and rubber mulches do not decompose, so they never need topping up, but they also never improve the soil, they can raise soil temperature considerably in sun, and they are difficult to remove once you change your mind. Match the choice to whether you want a soil amendment or a permanent ground cover. Homemade compost and leaf mold work well as mulch and close the loop on yard waste, though partially finished compost can carry weed seed. On landscape fabric under mulch: it holds back existing weeds at first, but as organic mulch breaks down on top of it, it forms a fresh seedbed above the fabric, and weeds happily root in that layer while the fabric blocks the mulch from ever reaching the soil below. Many gardeners find it makes beds harder to maintain over a few years, not easier. Two last checks. Keep mulch away from wood siding and foundations, since a permanently damp layer against the structure is an invitation to rot and to insects that were already looking for a way in. And if you are ordering bulk from a new supplier, ask what the material is and whether it has been aged — very fresh, hot material can be sour enough to damage tender plants if spread thickly right away.