Mulch Calculator
Result
Volume
- Volume in cubic yards
- 1.85 yd³
- Bags of mulch (2 cu ft each)
- 25
Mulch is sold by the cubic yard in bulk and by the 2 cubic foot bag at the garden centre, and this mulch calculator gives you both numbers from the same area and the same depth. Enter the flower bed, choose the depth — three inches holds weeds down without smothering the roots under it — and read off the cubic feet, the cubic yards and the bags of mulch to buy. Bark, wood chips and straw are all measured the same way, which is why this page never asks which one you are spreading: the volume is the same answer either way.
Mulch per 100 square feet
| Depth (in) | Cubic feet per 100 ft² | Bags per 100 ft² |
|---|---|---|
| 1 | 8.33 | 5 |
| 2 | 16.67 | 9 |
| 3 | 25 | 13 |
| 4 | 33.33 | 17 |
Bags are the 2 cubic foot size sold at a garden centre, rounded up. Read across from the depth, then scale to your bed: half the area is half the bags.
Formula
Volume (ft³) = length (ft) × width (ft) × mulch depth (in) ÷ 12
- L
- Length of the bed, in feet
- W
- Width of the bed, in feet
- D
- Depth of mulch to spread, in inches
Use it for a flower bed, a shrub border, a tree ring or a vegetable patch. Two to four inches is the working range: thinner and the weeds come through, thicker and rain stops reaching the roots. Keep the mulch a hand's width clear of trunks and stems, and measure the bed as a rectangle even when it curves — the error is far smaller than the rounding you do at the till.
Worked examples
A 20 ft by 10 ft flower bed, three inches of mulch
- Area: 20 × 10 = 200 square feet
- Depth in feet: 3 ÷ 12 = 0.25 ft
- Volume: 200 × 0.25 = 50 cubic feet
- In cubic yards: 50 ÷ 27 = 1.85
- Bags: 50 ÷ 2 = 25 bags of 2 cubic feet
Twenty-five bags is close to half a ton to carry from the car, while 1.85 cubic yards is the same material tipped in one delivery — if a wheelbarrow can reach the bed, bulk wins on both money and back.
A 40 ft by 4 ft border, two inches of mulch
- Area: 40 × 4 = 160 square feet
- Depth in feet: 2 ÷ 12 = 0.167 ft
- Volume: 160 × 0.167 = 26.7 cubic feet
- In cubic yards: 26.7 ÷ 27 = 0.99 — just under one yard
- Bags: 26.7 ÷ 2 = 13.3, so buy 14
The bag count rounds up, always: 13.3 bags means 14, because the part-bag at the end has to be bought whole. Two inches is a top-up depth for a bed that already has mulch in it.
Limitations
The bed is treated as a rectangle. A curved border, a tree ring, or a bed with shrubs already in it takes less than the full area suggests — either subtract the ground the plants occupy or order about 10% less. Depth is the settled depth, and mulch settles by roughly a fifth in the first season, so plan on topping up rather than ordering extra deep in spring. Bulk mulch is sold by the cubic yard and bagged mulch by the cubic foot: a 2 cubic foot bag is 0.074 of a cubic yard, so it takes 13.5 bags to make a yard, which is why bags cost several times more per cubic foot than a delivery.
Frequently asked questions
- How much mulch do I need?
- Area in square feet times depth in feet, then divide by 27 for cubic yards — or by 2 for the number of 2 cubic foot bags. A 200 square foot flower bed at three inches is 50 cubic feet, which is 1.85 cubic yards or 25 bags. Nothing about the shape of the bed changes the arithmetic, only the area.
- How deep should mulch be?
- Two to four inches for most beds, with three as the usual choice. Under two inches the weeds push through and the soil dries out faster than bare ground in the sun; over four inches the mulch mats together and sheds rain before it reaches the roots. A thin inch is enough for a top-up over last year's layer.
- How many bags of mulch are in a cubic yard?
- Thirteen and a half bags of 2 cubic feet. That is the number that decides how you buy: a cubic yard delivered in bulk is one tipping load, and the same volume in bags is fourteen trips to the car — which is why bags only make sense for a bed you can cover with a handful of them.
- How many cubic feet are in a cubic yard of mulch?
- Twenty-seven, because a yard is three feet. So a bed that needs 50 cubic feet needs 1.85 cubic yards, and a supplier selling in whole yards will send two. Rounding up a quarter of a yard is cheap; running short halfway along a border means a second trip.
- Should mulch touch the trunk of a tree?
- No — keep it a hand's width clear of the trunk and of the stems of shrubs. Mulch piled against bark holds moisture there, and that is where rot and rodent damage start. A tree ring should look like a shallow saucer, not a cone; the cone of mulch against a trunk is the single most common mistake with this material.
- Is wood chips the same as bark mulch?
- They behave differently. Bark breaks down slowly and knits into a mat that holds well on a slope; wood chips are coarser, last longer, and are the usual choice for a path or a play area. Both measure the same by volume, so the numbers on this page are right either way — the choice is about how the bed looks and how fast it needs topping up.
References
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811 — the cubic foot and cubic yard factors used for the volume and for the bag count — National Institute of Standards and Technology
- Approximate Conversions from U.S. Customary Measures to Metric — the working chart for feet, inches and cubic feet — National Institute of Standards and Technology