Understanding your result
The big number is the total volume to buy, with your extra allowance already added. Bulk suppliers sell by the cubic yard or the cubic meter, so that is the unit you will quote on the phone. Underneath it, the same volume is turned into whole bags of the size you picked.
Both figures are rounded up, never down. Half a bag short means a bare patch and a second trip, while half a bag over disappears into the bed without anyone noticing. Bulk orders are rounded to the next half cubic yard (or quarter cubic meter) because that is how most yards sell it. If your supplier only sells whole yards, round up again.
The weight line is there for one reason: hauling. It is a wide range on purpose. Dry shredded bark is light, and the same mulch after a week of rain can weigh twice as much. Use the heavy end when you decide whether your trailer or pickup can carry the load.
If you entered prices, the last rows compare the two ways of buying. The bag cost is the number of bags times your price. The bulk cost is the rounded bulk quantity times the price per yard, plus delivery.
How we calculate this
The sum is area times depth, with the depth converted into the same unit as the area.
The area depends on the shape you choose:
- Rectangle: length × width
- Circle: 3.1416 × radius × radius, where the radius is half the diameter
- Triangle: base × height ÷ 2, with the height measured square to the base
If you have several beds of the same size, the area is multiplied by the number of beds before anything else happens. For beds of different sizes, run the calculator once for each and add the results, or work out the total area yourself and use the “I know the area” option.
In metric the sum is the same with friendlier numbers: square meters × depth in centimeters ÷ 100 gives cubic meters, and one cubic meter is 1,000 liters.
The assumptions behind the numbers
| Assumption | Value used | Why |
|---|---|---|
| Cubic yard | 27 cubic feet | A yard is 3 feet, and 3 × 3 × 3 = 27 |
| Bag sizes | 1.5, 2 and 3 cu ft; 50, 70 and 100 L | The sizes most garden centers stock. Check the bag, because some brands sell by weight instead |
| Extra allowance | 5% unless you change it | Covers uneven ground and settling. Raise it for slopes and rough soil |
| Bulk rounding | Up to the next 0.5 cu yd or 0.25 m³ | The smallest step most suppliers will load |
| Weight | 400 to 800 lb per cu yd (240 to 475 kg per m³) | Wood mulch varies widely with moisture and type. For hauling decisions only |
Assumptions last reviewed October 3, 2026.
The calculator does not choose the depth for you, because the right depth depends on the mulch. Fine or shredded mulch packs down and does its job at 2 to 3 inches (5 to 8 cm). Coarse bark nuggets leave more air between pieces and can go on at 3 to 4 inches (8 to 10 cm). Piling any mulch deeper than about 4 inches can keep water and air from reaching roots, so the calculator shows a warning past that point.
Two worked examples
Topping up a foundation bed
A bed along the front of a house measures 28 feet long and 5 feet deep. The old mulch has thinned to about an inch, so the plan is to add 2 inches of shredded bark.
- Area: 28 × 5 = 140 sq ft
- Volume: 140 × 2 ÷ 12 = 23.3 cu ft
- With 5% extra: 24.5 cu ft, which is 0.91 cu yd
- In 2 cu ft bags: 24.5 ÷ 2 = 12.25, so 13 bags
- In bulk: rounded up to 1 cu yd
Now the money. Say bags are $4.50 each and bulk bark is $38 a yard with a $60 delivery fee. Thirteen bags come to $58.50. One yard delivered comes to $98. For this bed, bags win.
The same prices also show where bulk takes over. A yard bought in bags costs 13.5 × $4.50 = $60.75, against $38 loose, a saving of $22.75 a yard. The $60 delivery fee is paid back after 60 ÷ 22.75 = 2.6 yards. So with these prices, anything from 3 yards up is cheaper in bulk.
A long border, in metric
A border is 9 meters long and 1.5 meters wide, and it is getting 7.5 cm of composted bark.
- Area: 9 × 1.5 = 13.5 m²
- Volume: 13.5 × 7.5 ÷ 100 = 1.01 m³
- With 5% extra: 1.06 m³, or 1,063 liters
- In 50 L bags: 1,063 ÷ 50 = 21.3, so 22 bags
- In bulk: rounded up to 1.25 m³
Twenty-two bags is a lot to carry from the parking lot. At this size a bulk bag or a loose delivery is worth pricing, even if it works out slightly more expensive, because it arrives at the curb in one go.
Common mistakes
- Mixing up units. Feet for the bed and inches for the depth is fine, as long as the inches are divided by 12. Multiplying 140 sq ft by “2” gives a number twelve times too big.
- Measuring the new depth instead of the top-up. If an inch of old mulch is still there and you want 3 inches in total, you are buying 2 inches, not 3.
- Mulching against trunks and stems. Keep mulch pulled back a few inches from tree trunks and shrub stems. A cone of mulch against bark holds moisture there and invites rot.
- Forgetting that bags are sold by volume, sometimes by weight. A “40 lb bag” tells you nothing about coverage. Look for cubic feet or liters on the label.
- Rounding down to save a bag. The last bag is the cheapest insurance in the whole job.
- Ordering by eye. A cubic yard looks small in a pile and enormous in a wheelbarrow. Trust the measurement, not the pile.
- Skipping the extra on slopes. Mulch creeps downhill and thins at the top. Allow 10% and expect to rake some back up after heavy rain.
Printable shopping list
Once you have a result, the Print shopping list button under the calculator opens a clean one-page list: the number of bags or the bulk quantity, the breakdown table, and the measurements you entered. Take it to the garden center, or read the bulk figure to the supplier when you phone in the order.
Before you go, check two things the calculator cannot know. First, the bag size on the shelf, since the same brand often sells two sizes side by side. Second, the supplier’s minimum delivery, which is commonly one or two yards. If your order is under the minimum, bags are the simpler choice.
Questions people ask
- How many bags of mulch are in a cubic yard?
- A cubic yard is 27 cubic feet, so it takes 13.5 bags of the common 2 cubic foot size, or 9 bags of the 3 cubic foot size. In metric, a cubic meter is 1,000 liters, which is 20 bags of 50 liters.
- How much area does one cubic yard of mulch cover?
- At 1 inch deep a cubic yard covers 324 square feet. At 2 inches it covers 162, at 3 inches 108, and at 4 inches 81 square feet. Divide 324 by your depth in inches to get the figure for any depth.
- How much does one 2 cubic foot bag cover?
- About 12 square feet at 2 inches deep, 8 square feet at 3 inches, and 6 square feet at 4 inches. A 50 liter bag covers about 1 square meter at 5 cm deep.
- Is bulk mulch cheaper than bags?
- Per cubic yard, bulk is almost always cheaper. The delivery fee is what changes the answer. For a small bed, bags usually win because there is no delivery charge. Enter your local prices in the calculator and it will compare the two totals for your quantity.
- Do I need to remove the old mulch first?
- Usually not. Old mulch that has broken down is doing the soil good. Rake it loose if it has matted, measure how deep it still is, and add only enough new mulch to reach your target depth. Enter that difference as the depth.
- Should I order extra?
- A little. The calculator adds 5% by default because beds are never perfectly level and mulch settles in the first weeks. On rough or sloping ground, 10% is more realistic.
Built and reviewed by Bertha
Last updated · How we work out our numbers