How to measure garden beds
Mulch is figured from bed area and depth. Measure each bed's length and width in feet and multiply. For curved beds, estimate with rectangles and circles using the square footage calculator, then enter the total area here. Around trees, measure the diameter of the mulch ring and use the circle option.
How deep to spread mulch
Many university extension services recommend a layer of about 2–3 in for most beds. Thinner layers do less to block weeds and hold moisture. Much thicker layers can keep water and air from reaching roots. Keep mulch pulled a few inches back from tree trunks and plant stems; piling it against the bark (often called a "mulch volcano") can lead to rot and pests.
If you are topping up last year's mulch, measure how much is left and only add the difference. An inch of fresh mulch over old mulch is often enough to refresh the color.
The formula
Cubic feet = area × depth (in) ÷ 12. Cubic yards = cubic feet ÷ 27. Bags = cubic feet ÷ bag size, rounded up.
Worked example
Three beds along a house add up to 240 sq ft, and you want 3 in of mulch:
- 240 × 3 ÷ 12 = 60 cu ft
- 60 ÷ 27 = 2.22 cubic yards
- 2 cu ft bags: 60 ÷ 2 = 30 bags
- 3 cu ft bags: 20 bags
At that size, it is worth getting a bulk price for 2.25 or 2.5 yards delivered and comparing it to 30 bags.
Waste and overage
Mulch is forgiving, and the calculator does not add waste by default. Fluffy, freshly shredded mulch settles a bit after rain, so if you want a full 3 in after settling, buying about 10% more is reasonable. Irregular beds also tend to be bigger than they look, so round up rather than down.
Common mistakes
- Going too deep. More is not better past about 3–4 in.
- Mulch against trunks and siding. Leave a gap around trees, and many pest-control guides suggest keeping organic mulch a short distance away from the house foundation.
- Skipping weeding. Pull existing weeds first. Mulch slows new weeds but does not kill established ones.
- Confusing yards and bags. One cubic yard equals 13.5 of the common 2 cu ft bags.
Buying tips
- Bagged mulch is most often sold in 2 cu ft bags, with some brands offering 1.5 or 3 cu ft. The bag size is printed on the label. Choose it in the calculator.
- Bulk mulch is sold by the cubic yard. Delivery fees can make bags cheaper for small jobs and bulk cheaper for large ones. Compare total cost.
- Dyed, shredded hardwood, pine bark nuggets, pine straw and cedar all wear differently. Larger nuggets last longer but can float away on slopes.
- Landscape fabric is optional. Many gardeners skip it in planting beds where they add or move plants often.
Weed barrier under mulch