The short answer
A 1,000 square foot garden area takes about 3.1 cubic yards of compost at 1 inch deep, and about 6.2 cubic yards at 2 inches. If you are topping off beds with a half inch, figure a little over 1.5 yards for that same 1,000 square feet.
Our compost calculator does this math for you. Enter the area and depth and it returns cubic yards to order.
Those numbers come from one piece of arithmetic that works for any bed, any depth. Once you have it, you never have to guess again, and you will stop ordering two yards for a job that needed five.
The formula, written two ways
Compost is sold by the cubic yard. A cubic yard is 27 cubic feet, which is a cube three feet on every side. The whole problem is converting an area in square feet and a depth in inches into that unit.
Version one, the fast one. Square feet times depth in inches, divided by 324, equals cubic yards.
So a 1,000 square foot area at 1 inch is 1,000 x 1 = 1,000, divided by 324, which is 3.09 yards. Round that to 3.1. At 2 inches it is 2,000 divided by 324, or 6.17 yards. Call it 6.2.
Where does 324 come from? There are 27 cubic feet in a yard, and 12 inches in a foot. Multiply 27 by 12 and you get 324. That single number does both conversions at once, which is why it is worth memorizing.
Version two, the one that shows its work. Length in feet, times width in feet, times depth in inches divided by 12, all divided by 27.
A bed that is 20 feet by 4 feet at 3 inches deep works out like this. 20 x 4 = 80 square feet. 3 inches divided by 12 is 0.25 feet. 80 x 0.25 = 20 cubic feet. Divided by 27, that is 0.74 cubic yards.
Both versions give the same answer. Use whichever one you can remember standing in the driveway with a tape measure. If the math is getting away from you because the yard has odd shapes, break the space into rectangles, run the numbers on each one, and add the results.
Measuring an area that is not a rectangle
Most real yards are not tidy rectangles. A few shortcuts cover almost everything you will run into.
- Circles. Measure from the center to the edge, square that number, and multiply by 3.14. A circular bed with a 6 foot radius is 6 x 6 x 3.14, or about 113 square feet.
- Triangles. Base times height, divided by 2.
- Curved borders. Pretend the curve is a rectangle using the average width. A border that wanders between 3 and 5 feet wide along a 40 foot run is close enough to 4 x 40, or 160 square feet.
- Odd blobs. Chop them into pieces you recognize and add up the pieces. Nobody is grading this.
Small errors in area matter less than you think, because an inch of depth in either direction changes the total far more than a foot of width does.
Size chart by area and depth
These are cubic yards, rounded to one decimal. Find your square footage, then your target depth.
| Area | 0.5 in | 1 in | 2 in | 3 in | 4 in |
|---|---|---|---|---|---|
| 100 sq ft | 0.2 | 0.3 | 0.6 | 0.9 | 1.2 |
| 250 sq ft | 0.4 | 0.8 | 1.5 | 2.3 | 3.1 |
| 500 sq ft | 0.8 | 1.5 | 3.1 | 4.6 | 6.2 |
| 750 sq ft | 1.2 | 2.3 | 4.6 | 6.9 | 9.3 |
| 1,000 sq ft | 1.5 | 3.1 | 6.2 | 9.3 | 12.3 |
| 1,500 sq ft | 2.3 | 4.6 | 9.3 | 13.9 | 18.5 |
| 2,000 sq ft | 3.1 | 6.2 | 12.3 | 18.5 | 24.7 |
Notice how fast the right side of that chart climbs. Going from 1 inch to 4 inches across 2,000 square feet is the difference between a pickup load and a full dump truck. Depth is the decision that drives your order, so make it on purpose rather than by feel.
How deep should the compost go
There is no single right depth. It depends entirely on what the compost is doing for you.
Top dressing an established lawn, about 0.25 to 0.5 inch. You are feeding soil life and improving structure, not burying grass. Anything thicker than a half inch starts smothering the turf you are trying to help. Spread it thin, rake it so the blades show through, and water it in.
Refreshing existing beds, 1 to 2 inches. Perennial beds settle and lose volume every season. A 1 inch layer laid on top each spring keeps soil biology working without disturbing roots. Two inches is reasonable in beds that have gone a few years without attention.
Vegetable gardens, 2 to 3 inches worked in. Annual vegetables are heavy feeders, and the beds get emptied and replanted every year anyway. Two to three inches turned into the top 6 to 8 inches of soil is the standard approach.
New beds in poor or compacted soil, 2 to 4 inches tilled in. This is the heaviest application and the one where people routinely under order. If you are converting lawn or builder fill into a planting bed, 3 to 4 inches mixed into the existing soil is what actually changes the texture. A thin skim on top of hardpan clay does very little.
Filling a raised bed from empty. Do not use compost alone. A blend is better, commonly something in the range of a third compost to two thirds topsoil or a bagged garden mix. Pure compost in a tall box settles hard and dries out oddly. For the volume math on the soil portion, the same formula applies, and topsoil and garden soil is sold by the same cubic yard.
Bagged compost versus bulk by the yard
This is where the numbers get uncomfortable for anyone standing in a garden center aisle.
A cubic yard is 27 cubic feet. Most bagged compost comes in 1.5 cubic foot bags. That means 18 bags equal one cubic yard. If you are doing 1,000 square feet at 2 inches, you need 6.2 yards, which is roughly 112 bags.
That is a lot of trips, a lot of plastic, and a lot of lifting. Bulk compost is almost always noticeably cheaper per yard than the bagged equivalent, and it arrives in one drop instead of twelve carloads. The rough break point is somewhere around one cubic yard. Below that, bags are fine and often more convenient. Above two or three yards, bulk wins on cost, time, and your back.
Bags still have their place. They are useful for topping off a few containers, for storing a reserve in the garage, and for jobs where you cannot get a truck anywhere near the work. For anything bed sized, order bulk compost by the yard and be done with it.
One practical note on bulk. Compost is heavier than mulch, and wet compost is heavier still. A yard of it is a real load. Plan where the pile goes before the truck arrives, ideally on a tarp on the driveway within easy wheelbarrow distance of the beds.
Why the pile shrinks and how much to round up
Two things work against you after delivery, and both argue for ordering a little extra.
First, compost settles. The material is loose and fluffy in the pile and in the bag. Once it is spread, raked, walked on, and rained on, it compacts. A layer you laid down at 2 inches can read closer to 1.5 inches a few weeks later. That is not a defect, it is just what organic material does as the air pockets collapse.
Second, compost keeps breaking down. It is finished enough to use, but the decomposition is not finished forever. Over a season, the organic matter continues to reduce in volume as soil organisms work on it. That is the whole point of the stuff, and it is also why beds need topping off again next year.
There is also simple waste. Some stays in the wheelbarrow, some ends up on the lawn, some gets lost in the corners.
So round up. A modest cushion on top of your calculated number covers settling, spillage, and the spot you measured a little short. On small jobs, round up to the next quarter yard. On larger jobs, add a bit and then round to the next whole yard, since most suppliers sell in whole or half yard increments anyway. Running out when you are three quarters finished means either a second delivery fee or a visibly uneven bed.
Having a little left over is not a problem. Spare compost goes into containers, around shrubs, into the bottom of planting holes, or into a corner of the yard where you will use it next month.
A few things that throw the math off
Existing mulch. If your beds already have 2 inches of bark on top, you have a decision to make. You can rake the mulch aside, apply compost to the soil, and put the mulch back, or you can spread compost over the top and let it work down. Either way, do not include the mulch depth in your compost calculation.
Plants in the bed. A perennial bed that is full of crowns and stems has less open soil than its square footage suggests. Measuring the full rectangle gives you a comfortable cushion rather than a shortfall, which is fine.
Slope. Sloped ground has more surface area than its footprint and compost tends to migrate downhill. Add a little on hillside beds and keep the layer on the thin side so it stays put.
Mixing in versus laying on. If you are tilling compost into existing soil, the depth in the formula is the depth of compost you are adding, not the depth you are tilling to. Three inches of compost worked into 8 inches of soil still uses 3 inches in the math.
Ordering checklist
Before you call in the order, run through this.
- Measure each bed and write down the square footage. Break odd shapes into rectangles and circles.
- Pick a depth based on the job, not on habit. Half an inch for lawn top dressing, 1 to 2 inches to refresh beds, 2 to 4 inches for new beds in rough soil.
- Run the numbers. Square feet times depth in inches, divided by 324.
- Add every bed together into one total so you pay for one delivery instead of two.
- Round up for settling and spillage. Next quarter yard on small jobs, next whole yard on big ones.
- Pick the drop spot in advance. Flat, close to the work, and out of the way of cars.
- Have a tarp, a wheelbarrow, a square shovel, and a hard rake ready before the truck shows up.
Get the depth decision right and the rest is arithmetic. Three and a bit yards per 1,000 square feet per inch is the number worth carrying around in your head.
How We Started
We started Mulch Mound because we got tired of the hassle that came with buying landscaping materials. The options were either loading bags into your car at a garden center or calling around to local suppliers, trying to figure out pricing, minimums, and delivery schedules. Neither option felt convenient or transparent.
Three of us – Alec, Mo, and Tyler – decided there had to be a better way. Alec and Tyler got their start back in 2013 running a landscaping business during college, moving mulch and mowing lawns to pay tuition. That experience taught them how frustrating it was to source materials, and years later, that frustration turned into Mulch Mound.
We focus on making it simple to get mulch, stone, and soil delivered directly to your home. Order online, pick your delivery date, and we handle the rest. No loading bags. No calling multiple suppliers. No wondering if you bought enough or paid a fair price.
We work with quality local suppliers in the areas we serve and aim to be straightforward about what we offer and what it costs. Landscaping is hard work. Buying the materials for it shouldn't be.
FAQ
How do I calculate cubic yards of compost?
Multiply the area in square feet by the depth in inches, then divide by 324. The 324 is 27 cubic feet per yard times 12 inches per foot, so it handles both conversions in one step. If you prefer thinking in feet the whole way, convert your depth to feet first by dividing inches by 12, multiply length by width by that depth, then divide by 27.
Should I order extra compost to account for settling?
Yes. Loose material compacts once it is spread and watered, and some of every load is lost to the wheelbarrow and the lawn. A modest cushion over your calculated figure is cheap insurance compared to paying a second delivery charge to finish the last quarter of a bed.
How many bags of compost equal a cubic yard?
Eighteen bags at 1.5 cubic feet each, since a cubic yard is 27 cubic feet. If your bags are a different size, divide 27 by the bag volume printed on the label. A 2 cubic foot bag means 13.5 bags per yard, and a 1 cubic foot bag means 27.
How much compost do I need for a 4x8 raised bed?
A 4 by 8 bed is 32 square feet. At 3 inches of compost that is about 0.3 cubic yards, or roughly 8 cubic feet. Filling that same bed from empty to 10 inches deep is a different question and takes close to 27 cubic feet of material, which is why raised bed fill is usually a blend rather than straight compost.
Can you put too much compost on a garden?
You can. Piling thick layers on year after year builds up excess nutrients and can hold too much moisture around plant crowns. On lawns especially, a layer thicker than about half an inch smothers the grass instead of feeding it. Annual thin applications beat occasional heavy ones.
Is it cheaper to buy compost in bulk?
For anything past a yard or so, yes, and the gap widens as the job grows. Bagged product carries the cost of the packaging and the handling. The practical tipping point is usually around one cubic yard, which is about 18 bags and several car trips.