How to use
- Pick the shape of the bed: a rectangle, a circle, a ring around a tree, or an area you already know.
- Enter the sizes, the type of mulch, and the depth you want.
- If there's old mulch, enter how deep it still is. Then select "Calculate".
How deep should mulch be?
| Mulch | Maximum depth |
|---|---|
| Shredded wood and fine bark | 2 to 3 inches |
| Coarse bark nuggets and chips | Up to 4 inches |
| Shredded leaves and grass clippings | No more than 2 inches |
These limits come from Clemson Cooperative Extension, which notes that coarse mulches let air move through them and so can go deeper than fine ones. UF/IFAS Extension in Florida recommends 3 inches and advises against applying more. The calculator warns you if the depth you enter is over the limit for the mulch you picked.
How far a cubic yard goes
One cubic yard covers 324 square feet at 1 inch deep. Divide 324 by your depth in inches to see what one yard covers:
| Depth | 1 cubic yard covers | 2 cu ft bags per yard |
|---|---|---|
| 1 inch | 324 sq ft | 13.5 |
| 2 inches | 162 sq ft | 13.5 |
| 3 inches | 108 sq ft | 13.5 |
| 4 inches | 81 sq ft | 13.5 |
The coverage figures match the University of Georgia Extension conversion tables. A yard is always 13.5 bags of 2 cubic feet or 9 bags of 3 cubic feet, whatever the depth.
Example: a bed 12 ft by 9 ft is 108 square feet. At 3 inches deep that's exactly 1 cubic yard, or 14 bags of 2 cubic feet once you round up.
Topping up old mulch
Mulch breaks down over time, so a bed often needs a top-up rather than a full new layer. Measure what's left and enter it under "Mulch already there". If a bed still has 1 inch and you want 3, you only need 2 inches of new mulch. For a 500 square foot bed, that's 3.09 cubic yards instead of 4.63.
Mulching around trees
- Clemson Extension advises keeping mulch 2 to 3 inches away from the stems of woody plants and never piling it against a tree trunk. For large trees, UF/IFAS suggests leaving about a foot clear around the base.
- Use the "Ring around a tree" shape and enter the bare circle you'll leave at the trunk. The calculator subtracts it.
- UF/IFAS recommends a mulched circle at least 8 feet across around a tree, and out to the drip line if you can.
- Keep mulch 6 to 12 inches away from the walls of your house, according to Clemson Extension.
Buying tips
- Bags are sold in 2 and 3 cubic foot sizes most often. Check the bag; the size is printed on the front.
- Bulk mulch is sold by the cubic yard. Past 3 or 4 yards, bulk is usually cheaper than bags.
- Fresh, wet mulch is heavy. If you're hauling it in a pickup, ask the supplier how much a yard weighs that day.
Common mistakes
- Piling it on. More is not better. Stay within the depth limits above.
- Volcano mulching. Mounding mulch up against a tree trunk is exactly what Clemson Extension warns against. Pull it back from the bark.
- Measuring only the long sides. For odd-shaped beds, break them into rectangles and circles, add the areas, and use "I know the area".
Sources
Depth limits and spacing: Clemson Cooperative Extension Home & Garden Information Center, Mulch. Florida guidance and tree rings: UF/IFAS Gardening Solutions, Choosing and Installing Mulches. Coverage table: University of Georgia Extension Bulletin B931. Unit conversions: NIST.
Related calculators
- Topsoil Calculator - soil for new beds before you mulch
- Gravel Calculator - stone instead of mulch for paths and borders
- Paver Calculator - pavers, base, and sand for a patio
- Percentage Calculator - compare prices of bags and bulk
Frequently asked questions
How many bags of mulch make a cubic yard?
13.5 bags of 2 cubic feet or 9 bags of 3 cubic feet make one cubic yard, since a cubic yard is 27 cubic feet.
How many square feet does a yard of mulch cover?
324 square feet at 1 inch deep, 162 at 2 inches, 108 at 3 inches, and 81 at 4 inches.
How thick should mulch be?
Clemson Extension recommends no more than 2 to 3 inches of fine wood or bark mulch, up to 4 inches of coarse nuggets, and no more than 2 inches of leaves or grass clippings.
Do I need to remove old mulch first?
Usually not. Measure how deep the old layer still is and enter it. The calculator orders only the difference. If the old layer is matted, rake it loose first.
How close to the tree trunk can mulch go?
Keep it off the trunk. Clemson Extension says to keep mulch 2 to 3 inches from the stems of woody plants, and UF/IFAS suggests about a foot of clearance around large trees.