How much mulch for a 100 sq ft garden bed?
0.9 cu yd of mulch for a 100 sq ft garden bed, at the settings most people start with. Below the calculator are the same numbers for the alternatives you are likely to choose, and what each one does to the total.
Reviewed · Method: measured dimensions, industry coverage rates, rounded up to real package sizes · How the numbers are calculated
Values are pre-filled for this page. Change anything and hit Recalculate.
The answer, and what it is made of
100 sq ft at 3 in deep is 0.9 cu yd of mulch, or 13 of bagged product. Bulk is roughly a third of the bag price per cubic foot, so at this size a bulk load already beats the bags — if you can take delivery where the pile is going.
Planning figure for everything on that list: $26 to $79, with $44 as the realistic middle for the products most people actually buy. These are estimates for budgeting, not quotes. Prices move by region and by season, and the middle figure assumes a mid-range product rather than the cheapest thing on the shelf.
Depth moves the number faster than area: 0.9 cu yd at 3 in depth becomes 1.2 cu yd at 4 in depth. On a footprint this size, one extra inch of depth is worth more than making it a tenth larger.
What changes if you change one thing
| Change the mulch depth | You buy |
|---|---|
| 2 in depth, thin refresh | 0.6 cu yd |
| 3 in depth, the standard | 0.9 cu yd |
| 4 in depth, smothering weeds | 1.2 cu yd |
Every row is a live calculation, not an estimate. The shaded row is what this page defaults to.
What goes in the cart
| Item | Quantity |
|---|---|
| Mulch (bulk, delivered) | 0.9 cu yd |
| Or 2 cu ft bags | 13 bags |
| Pre-emergent herbicide | 1 lb |
| Garden edging | 50 ft |
| Wheelbarrow + pitchfork | 1 each |
Three inches is the number. Less than two inches and weeds push through. More than four inches and you smother the root zone and invite fungus. Keep it off the trunk by a hand's width.
What this size actually changes
One hundred square feet at 3 in deep is 25 cubic feet, or just under a cubic yard. That is exactly the crossover point: a yard of bulk mulch costs about a third of thirteen bags per cubic foot, so 100 sq ft is the size where bulk starts to win — provided you can take a pile where it needs to go, which is the part that decides it in practice.
Figure. 100 sq ft garden bed: 20 x 5 ft. Measure the finished surface, not the room walls — the area between skirting or cabinet faces is the area you pay for.
How the quantity is worked out
Mulch is sold by the cubic foot in bags and by the cubic yard in bulk, and the depth is what you are really buying. Three inches is the useful depth: enough to suppress annual weeds and hold moisture, shallow enough that rain still reaches the soil. Two inches is a refresh over existing mulch, four inches smothers weeds but also starves roots of oxygen if you keep topping it up.
Bulk is roughly a third of the bag price per cubic foot, so the break-even is usually around one cubic yard. Below that, bags are simpler. Above it, bulk plus a delivery charge is still cheaper — and one cubic yard of mulch covers about 100 sq ft at three inches.
How to measure this job
Measure the bed in whatever shapes it actually is. Straight beds are length times width; curved beds are best estimated as a series of rectangles; beds that wrap around shrubs should have the shrub footprint subtracted. A bed that looks like 100 sq ft is often 80 once the plants are taken out.
Depth is the second measurement and the one that matters most. Check the existing mulch depth with a trowel before ordering: if it is already at three inches, you are refreshing, not mulching, and the quantity needed is a fraction of a full application.
Mistakes that cost real money
Piling mulch against the trunk
Mulch volcanoes kill trees slowly. Moisture held against the bark rots it, and roots grow up into the mulch instead of down into the soil. Keep a clear ring of two to three inches around every trunk, and never bury the flare where trunk meets root.
Mulching over weeds instead of removing them
Three inches of mulch suppresses annual weeds but does not kill perennial ones. Thistle, bindweed and dock push straight through. Clear them first, or you are feeding them.
Spreading 25 cu ft by the bag into a barrow
Thirteen bags is 25 cubic feet and around 500 lb of material. Doing it bag by bag into a wheelbarrow is four times the work of having a yard tipped close to the bed and moving it once. On 100 sq ft the delivery is worth it if access allows.
Mulching right up to the stems of perennials
Three inches of mulch against a soft stem holds moisture where it does the most damage. Pull it back an inch or two around each plant. The bed still suppresses weeds; the plants stop rotting at the crown.
Frequently asked questions
How many bags of mulch is a cubic yard?
Thirteen and a half bags of 2 cu ft, or nine bags of 3 cu ft. Bulk mulch is priced by the yard and is usually about a third of the bag price per cubic foot, so if you need more than a yard, bulk plus delivery is normally cheaper than bags.
How many bags of mulch for 100 sq ft?
At three inches deep, 25 cubic feet, which is thirteen 2 cu ft bags or nine 3 cu ft bags. At two inches it drops to about nine 2 cu ft bags. Depth changes the answer far more than area does.
How much mulch for 100 sq ft?
Twenty-five cubic feet at 3 in deep: thirteen 2 cu ft bags or nine 3 cu ft bags. At 2 in it drops to about 17 cu ft, and at 4 in it rises to 33, which is why depth is the first number to decide.
How long does 100 sq ft of mulch last?
Two to three years at 3 in, depending on the material. Bark and cedar break down slowly, straw and compost much faster. Top up to depth rather than adding a fixed amount, and check with a trowel before ordering.
What will the materials for this cost?
A planning range of $26 to $79 for everything in the shopping list, with $44 as the realistic middle. That is materials only: it excludes labour, delivery, tool hire and disposal of the old surface. Treat it as a budgeting figure, not a quote.