Landscaping
Topsoil Calculator
Enter the bed or the area and how deep it goes, and this tells you the volume to buy and how much of it should be compost.
| Area to fill | — |
|---|---|
| Depth, converted to feet | — |
| Volume needed | — |
| Divided by 27 cu ft per cu yd | — |
| Topsoil | — |
| Compost | — |
| Bags to buy | — |
UNITS CU FT
SOURCE /SOURCES/#topsoil
What to buy
Paid links. If you buy through one, we earn a commission. Your price is the same. Nothing is listed here unless the calculator above says you need it.
Why this is more than you need
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Bagged topsoil
The bag count above assumes the size you picked. Soil bags run smaller than mulch bags, so check the cubic feet on the front before you count.
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Bagged compost
The second half of the split. If you set the compost share above zero, this is the number of bags the calculator just worked out.
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Pre-mixed raised bed soil
Topsoil and compost already blended. Costs more per cubic foot than mixing your own, and the total volume you need does not change.
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Wheelbarrow
Worth it past about a cubic yard, which is 27 bags at 1 cu ft. Soil is heavier than mulch for the same volume.
What the extension services state
| Penn State Extension | 1 to 2 in, tilled in | 3.1 to 6.2 cu yd per 1,000 sq ft, before seeding turf |
|---|---|---|
| Penn State Extension | about 1/4 in | topdressing established turf, worked into the soil |
| Wisconsin Horticulture | 2 in, tilled in | before planting a vegetable bed |
| UMN Extension | 1/3 to 1/2 compost | the rest topsoil, in a raised bed |
Not a manufacturer spec, because nobody sells soil to one. These are the published rates from three university extension programs, which is the closest thing this material has to a standard.
Gear for the job
The calculator above does not count any of this. It is what the job takes to actually do. Paid links, and your price is the same.
- Digging fork Blending soil and compost in the bed is faster with a fork than a spade, and it does not pack the mix down while you work.
- Bow rake Depth is the whole calculation, and a bow rake is what turns a heap into an even two inches.
- Heavy-duty tarp Mix on the tarp rather than in the bed when the compost share is high, then drag it over. Beats twenty trips with a bucket.
- Soil test kit Worth doing before you buy amendments. It is the one number this calculator cannot work out for you.
- Garden gloves Bagged soil is wet, gritty and heavier than it looks. Fifty pounds a bag at 2 cu ft is normal.
Part of a bigger job
This calculator sizes one material. These jobs need it along with others, and the list says what else to buy and in what order.
- Plant a bed mulch, gravel
- Reseed a patchy lawn grass seed, starter fertilizer
The volume is only half the question. An 8 by 4 bed filled 10 inches deep takes about 27 cubic feet, and UMN Extension puts a third to a half of that as compost rather than straight topsoil. Buy one number and you have bought the wrong thing.
How to estimate topsoil and compost
Soil is sold by volume and spread by depth, so the arithmetic is area times depth. The trap is units. Your bed is in feet, your depth is in inches, and the soil is in cubic feet or cubic yards.
cubic feet = area (sq ft) × depth (in) ÷ 12
cubic yards = cubic feet ÷ 27Dividing by 12 turns inches into feet. Dividing by 27 turns cubic feet into cubic yards, because a cubic yard is 3 × 3 × 3 feet.
Measuring a raised bed
Measure inside the frame, not outside. A bed built from 2-inch lumber loses four inches across each direction, and on a 4 by 8 bed that is about 10 percent of the volume. Length times width gives the footprint.
For depth, use the height you intend to fill to rather than the height of the frame. Filling flush to the rim means soil on the path after the first watering. An inch or two of freeboard is normal, and it is why this calculator asks for fill depth instead of assuming the frame height.
Measuring ground you are covering
Rectangles are length times width. For an irregular patch, break it into rectangles and add them up. For a circle, radius times radius times 3.14. Being off by a foot on a border bed changes the answer by less than a bag.
How deep, and it depends on the job
There are three different jobs here and they use wildly different depths, which is why a single "topsoil depth" answer is useless.
Filling a raised bed. The depth is whatever the bed is, less your freeboard. Most beds are 10 to 12 inches. This is the case where the volume surprises people: a 4 by 8 bed at 10 inches is nearly a full cubic yard, which is 27 bags at a cubic foot each.
Preparing ground before planting or seeding. Penn State Extension puts compost incorporated before turf establishment at a one-inch to two-inch layer, which it states as roughly 3.1 to 6.2 cubic yards per 1,000 square feet. Wisconsin Horticulture gives two inches tilled in before planting a vegetable bed. So one to two inches, worked into the soil rather than left on top.
Topdressing an established lawn. A quarter inch. Penn State is explicit that a surface application on established turf should be a thin layer of about a quarter inch, worked into the soil. Pile it on thicker and you smother the grass you are trying to help. A quarter inch over 1,000 square feet is under a cubic yard, which is far less material than most people buy.
The mix nobody mentions
This is the part a bag of soil will not tell you. A raised bed is not filled with topsoil alone. UMN Extension states the ideal mixture as around one half to two thirds topsoil and one third to one half compost.
That changes what you buy, not how much. The total volume is the same either way. What moves is the split: at 27 cubic feet and a third compost, you are buying about 18 cubic feet of topsoil and 9 of compost, and those are two different products on two different pallets. Set the compost share above and the calculator counts both bag piles separately, because that is how you will actually be standing at the register.
Pre-mixed garden soil is the same two things already blended. It costs more per cubic foot and saves you the mixing. The volume does not change.
Bags or bulk
A cubic yard is 27 cubic feet. Soil is commonly bagged at 0.75 or 1 cubic foot, smaller than the 2 cubic foot bags mulch comes in, so the same volume is roughly twice as many bags and each one is heavier. A cubic foot of damp topsoil runs about 40 pounds.
Under a cubic yard, bags win. They fit in a car, you can store the extras, and you open only what you need. Past about two cubic yards you are opening 50 or more bags, and bulk delivery is usually cheaper per yard and far less work. That crossover is a handling judgment rather than a spec, so price both.
One caution on bulk: a yard of soil is a much bigger pile than a yard of mulch feels like, and it weighs roughly a ton. Make sure it can be dumped somewhere you can actually work from.
What one cubic yard covers
Worth carrying in your head, because it turns a delivery quote into a picture of your yard. One cubic yard spreads to 324 square feet at 1 inch deep. That is just 27 divided by one twelfth. Halve it for 2 inches, so 162 square feet. At the quarter inch used for topdressing a lawn, one yard covers about 1,300 square feet.
A quick cost check
Take that 4 by 8 bed at 10 inches, with a third of the fill as compost. The bed needs 26.7 cubic feet, so 18 bags of topsoil and 9 of compost at a cubic foot each. At $5 a bag that is $135. The same volume delivered as bulk soil at about $50 a yard is around $50 plus a delivery fee, but it is a full yard dumped on your driveway for a single bed. For one bed, bags win. For four beds, they do not.
Common estimating mistakes
- Measuring the outside of the frame. On a 4 by 8 bed built from 2-inch lumber, the inside is about 3 ft 8 in by 7 ft 8 in, which is roughly 10 percent less soil.
- Forgetting to divide by 12. Multiplying 32 square feet by 10 gives 320, not 26.7. Depth has to be in feet before it multiplies cleanly into cubic feet.
- Buying it all as topsoil. The compost share is a real part of the order, not an optional extra, and it is a separate product to pick up.
- Topdressing a lawn too thick. A quarter inch is the published figure. An inch of soil over living grass is a different and worse job.
- Assuming every bag is the same. Soil is sold at 0.75, 1, 1.5 and 2 cubic feet on the same shelf, and the bag count nearly triples between the smallest and largest.
- Pricing in a settling factor. Nobody publishes one you can rely on. Fill, water, wait a week, top up.
When to hand it off
Filling beds is not dangerous work, so the honest boundary here is weight rather than skill. A cubic yard of soil is about a ton, and moving several yards by wheelbarrow is a genuinely hard day. Past three or four yards, pay for delivery to the closest point you can reach and get help.
The one thing worth handing off is diagnosis. If ground is staying wet, growing nothing, or dropping year after year, adding soil on top treats the symptom. Drainage and grading are their own trades, and a few inches of new topsoil will not fix either.
Questions
How much soil do I need for a 4x8 raised bed?
A 4 by 8 foot bed is 32 square feet. Filled 10 inches deep that is about 26.7 cubic feet, which is a shade under a cubic yard. Filled the full 12 inches it is 32 cubic feet. Then split it: UMN Extension puts the ideal raised bed mix at a half to two thirds topsoil and a third to a half compost, so at 10 inches deep and a third compost you want roughly 18 cubic feet of topsoil and 9 of compost.
How many bags of topsoil are in a cubic yard?
A cubic yard is 27 cubic feet, so it takes 27 bags at 1 cu ft, 36 bags at 0.75, 18 at 1.5, or 14 at 2. Bag sizes are not standard and soil is often bagged smaller than mulch, so read the cubic feet printed on the bag rather than counting bags from someone else's estimate.
What is the difference between topsoil, compost and garden soil?
Topsoil is mineral soil and it is the bulk of what fills a bed. Compost is decomposed organic matter and goes in as a share of the mix, not as the whole thing. Garden soil is the two already blended, sold ready to use at a higher price per cubic foot. The volume you need is the same whichever you buy, so the choice is about price and how much mixing you want to do.
How much topsoil do I need to level a lawn?
Less than people expect. Penn State Extension puts a surface application on established turf at about a quarter inch, worked into the soil rather than left sitting on the grass. A quarter inch over 1,000 square feet is under a cubic yard. Deep low spots are a separate job: fill those first, then topdress the whole area.
Does bagged soil settle after you fill a bed?
Yes, and nobody publishes a settling figure you can trust, so this calculator does not pretend to have one. Bagged soil is loose when you open it and compacts once it is watered. Buy the volume you calculated, fill to an inch below the rim, water it in, then top up in a week if it has dropped. That is more accurate than adding a made-up percentage now.
Every constant on this page is logged with its source and the date it was checked on the sources page.