Topsoil, garden soil and compost are not interchangeable
Suppliers use these words differently, and the difference changes both the depth you plan and the price you pay. As a working distinction: topsoil is mineral soil, usually screened, sold to add or rebuild the growing layer; garden soil or planting mix is normally a topsoil and compost blend intended to be planted straight into; compost is decomposed organic matter, used as an amendment rather than as a growing medium on its own.
Because the words travel loosely, the label matters more than the name. A product sold as garden soil may already contain enough organic matter that adding more compost would be wrong, and a cheap topsoil may be mostly subsoil with little organic content. Ask what the product is screened to and what it is blended from before deciding a depth.
Depths by use: the number that actually matters
Topsoil depth is where projects go wrong. Half an inch spread over an established lawn is a soil amendment; half an inch in a raised bed is not enough to grow anything. The calculator carries a preset for each of the common uses and warns you when your depth sits outside its planning range.
| Use case | Planning range | Default | Note |
|---|---|---|---|
| Garden bed | 4–8 in | 6 in | Depth to add on top of existing ground. |
| Raised bed fill | 6–24 in | 12 in | Use the inside height of the bed. Soil settles over time. |
| Lawn top-dressing | 0.25–0.5 in | 0.5 in | A thin layer is spread over the existing lawn. |
| New lawn | 3–6 in | 4 in | Depth varies with existing soil quality. |
Planning ranges, not site-specific specifications. Your soil, drainage and use can justify a different depth.
- Lawn top-dressing is deliberately thin. Spreading too deep smothers the grass you are trying to help.
- A planting bed is usually improved rather than replaced, so the added depth is measured on top of what is already there.
- A raised bed is filled to a depth, so the number you want is the inside height you intend to fill, not the height of the boards.
- A new lawn on poor subsoil needs the most material of the four, and the depth depends on how much existing soil is worth keeping.
Filling a raised bed without overshooting
A raised bed is the easiest topsoil project to calculate accurately, because the container defines the volume for you. Measure the inside dimensions and the fill height, and remember that soil settles: most beds are filled slightly proud and then topped up after a few weeks of watering.
| What people measure | Why it is wrong | What to measure instead |
|---|---|---|
| Outside length and width | Includes the wall thickness, which is dead space | Inside the boards, corner to corner |
| Full board height | Leaves a lip and ignores settling | The fill depth you actually want |
| One bed at a time | Misses the option of a single bulk delivery for all beds | Measure every bed, then add them as separate areas in one calculation |
Worked examples for the three common jobs
Each example below is calculated by the same engine the calculator uses, so you can reproduce it exactly by entering the same figures yourself.
Topping up a 10 ft × 20 ft planting bed by six inches
An existing planting bed is built up with 6 in of screened topsoil before replanting, using the calculator default 10% waste allowance.
Inputs
- Material
- Topsoil
- Area
- 10 ft × 20 ft
- Depth
- 6 in
- Waste
- 10%
Results
- Project area
- 200 sq ft18.58 m²
- Depth used
- 6 in
- Volume before waste
- 100 cu ft3.7 cu yd
- Waste allowance
- 10%
- Volume to order
- 110 cu ft4.07 cu yd · 3.11 m³
- Order quantity
- 4.25 cu ydRounded up to the nearest 0.25 cu yd
- Estimated weight
- 4.48 tons4.07 tonnes at the 1.1 tons/cu yd planning density
- 0.75 cu ft bags
- 147 bags
- 1 cu ft bags
- 110 bags
- 1.5 cu ft bags
- 74 bags
- Bags or bulk?
- Bulk delivery is usually easier at this volume
Six inches over this area is a serious amount of material, and the bag rows show why bagged soil rarely suits bed building. The result is a small bulk delivery, which is where the cost conversation starts rather than where it ends.
Filling a 4 ft × 8 ft raised bed to twelve inches
One raised bed is filled to 12 in of depth using its inside dimensions, with the raised-bed preset selected in the calculator.
Inputs
- Material
- Topsoil
- Area
- 4 ft × 8 ft
- Depth
- 12 in
- Waste
- 10%
Results
- Project area
- 32 sq ft2.97 m²
- Depth used
- 12 in
- Volume before waste
- 32 cu ft1.19 cu yd
- Waste allowance
- 10%
- Volume to order
- 35.2 cu ft1.3 cu yd · 1 m³
- Order quantity
- 1.5 cu ydRounded up to the nearest 0.25 cu yd
- Estimated weight
- 1.43 tons1.3 tonnes at the 1.1 tons/cu yd planning density
- 0.75 cu ft bags
- 47 bags
- 1 cu ft bags
- 36 bags
- 1.5 cu ft bags
- 24 bags
- Bags or bulk?
- Bags or bulk delivery are both reasonable
This is the calculation that proves the point about measuring inside dimensions. Fill depth, not board height, drives the number, and a single bed of this size still lands in the range where bags and bulk compete closely.
Top-dressing a 2,000 sq ft lawn at half an inch
An established lawn is top-dressed at ½ in over 2,000 sq ft, entered as a measured area with the lawn top-dressing preset selected.
Inputs
- Material
- Topsoil
- Area
- 2,000 sq ft measured area
- Depth
- 0.5 in
- Waste
- 10%
Results
- Project area
- 2,000 sq ft185.81 m²
- Depth used
- 0.5 in
- Volume before waste
- 83.33 cu ft3.09 cu yd
- Waste allowance
- 10%
- Volume to order
- 91.67 cu ft3.4 cu yd · 2.6 m³
- Order quantity
- 3.5 cu ydRounded up to the nearest 0.25 cu yd
- Estimated weight
- 3.73 tons3.39 tonnes at the 1.1 tons/cu yd planning density
- 0.75 cu ft bags
- 123 bags
- 1 cu ft bags
- 92 bags
- 1.5 cu ft bags
- 62 bags
- Bags or bulk?
- Bulk delivery is usually easier at this volume
| Depth | Volume to order | Order quantity | Estimated weight | Smallest bag size |
|---|---|---|---|---|
| 0.25 in | 1.7 cu yd | 1.75 cu yd | 1.87 tons | 62 bags |
| 0.5 in | 3.4 cu yd | 3.5 cu yd | 3.73 tons | 123 bags |
| 1 in | 6.79 cu yd | 7 cu yd | 7.47 tons | 245 bags |
Every column comes from the same calculation engine used by the calculator.
Thin applications are the opposite problem: the volume is small enough that bagged material is genuinely practical, and the bag rows confirm it. Together with the cross-check table above, this result shows why depth, not area, is the variable that decides how topsoil gets bought.
Cross-checking thin lawn applications against published guidance
Lawn top-dressing is the one topsoil job where an independent published figure is easy to find, so it is worth checking the calculator against it. Penn State Extension publishes a table of compost volumes per unit area for surface applications from one quarter inch up to two inches. The engine output below uses the same area and depths with the waste allowance set to zero, which is the basis a published table uses.
| Depth applied | Engine volume | Engine volume (cu yd) | Published table (cu yd) |
|---|---|---|---|
| 0.25 in | 208.44 cu ft | 7.72 | 8 |
| 0.5 in | 416.61 cu ft | 15.43 | 15 |
| 1 in | 833.22 cu ft | 30.86 | 31 |
| 1.5 in | 1,250.1 cu ft | 46.3 | 46 |
| 2 in | 1,666.71 cu ft | 61.73 | 62 |
The published table rounds to whole cubic yards, which is why the two columns differ in the decimals but agree on the number you would order.
The columns agree at every depth. That is a useful confirmation that the calculator uses the same arithmetic a land-grant extension service publishes. What a published table cannot tell you is what your own soil needs, which is why the depth setting stays in your hands.
Bags, bulk and how much waste to allow
Topsoil is usually ordered screened, by the cubic yard, and delivered loose. Bags are common for small repairs and for bagged blends. Because the material is usually spread by hand and raked to a grade, it deserves a slightly more generous waste allowance than a machine-spread aggregate.
| Assumption | Planning value |
|---|---|
| Typical density | 1.1 tons/cu yd |
| Density range seen in practice | 0.9–1.4 tons/cu yd |
| Bag sizes used for bag estimates | 0.75 cu ft, 1 cu ft, 1.5 cu ft |
| Default waste allowance | 10% |
| Order rounding | Nearest 0.25 cu yd |
Moisture and organic content change weight significantly.
- Waste covers soil that sinks into the existing surface, spills from a barrow, or is lost in a long carry from the drop point.
- Soil settles when it is watered, so a layer spread to exactly the target depth will be thinner a month later.
- The weight of a cubic yard depends heavily on moisture. Wet soil can weigh considerably more than dry, which affects how much a barrow holds and how far a truck can safely go.
Related planning pages
Keep going
- Topsoil, garden soil and compost comparedWhat the words mean and where suppliers differ
- What drives landscaping project costMaterial, delivery, labour and site preparation
- How to calculate mulchThe layer that often goes on top of new soil
- Open the Topsoil Calculator
Try it: Topsoil Calculator
Estimate topsoil for lawns, gardens and raised beds. Every number on this page came from the same engine, so you can replace the example figures with your own measurements and compare.
Frequently asked questions
How much topsoil do I need for a new lawn?
It depends on what is already there. If the existing soil is workable and reasonably drained, a few inches of blended material tilled in is often enough. If the subsoil is compacted, stony or poor, the added depth has to be larger. The calculator shows 3–6 in as a planning range for new lawn, with 4 in as the default, and lets you enter your own depth.
How deep should topsoil be over existing soil?
For planting beds, 4–8 in of added topsoil is the common planning band, and the right answer depends on how deep the roots you are planting will go. For a lawn top-dressing the number is far smaller: a quarter to half an inch at a time, repeated if needed rather than applied all at once.
Can I use topsoil for a raised bed?
Topsoil is usually the base component, and it is common to blend it with compost so the bed holds moisture and drains well. Suppliers sell pre-blended raised-bed mixes for exactly this reason. Use the inside dimensions of the bed and the depth you intend to fill, and treat the result as a volume rather than a recipe.
How many bags of topsoil make a cubic yard?
It depends on the bag. A cubic yard is 27 cu ft, so that is thirty-six 0.75 cu ft bags, twenty-seven 1 cu ft bags, or eighteen 1.5 cu ft bags. The calculator shows all three counts for your volume so you can compare a bag price with a bulk price honestly.
Does the calculator tell me how much compost to add?
No. Compost is used as an amendment, and how much to add depends on what the soil needs, which normally means a soil test. The calculator is for planning the volume of material you are spreading or filling.
Sources and references
- Penn State Extension — Using Composts to Improve Turf PerformancePublished surface-application volumes per unit area, used above as an independent cross-check on thin lawn applications.
These references support the general background on this page only. Product data, local requirements and site conditions take precedence over anything published here.
Method and limitations
Where this estimate stops being useful
The calculator models volume, not soil suitability. It does not test drainage, pH, organic content, compaction or contamination, and it cannot tell you whether a supplier product is adequate for planting. Screened topsoil can still contain weed seed, stones or a high clay fraction. If a lawn or a planting scheme depends on the result, get a soil test or an agronomic recommendation rather than inferring quality from a quantity.
The methodology page documents how volume, waste, compaction and purchase quantities are produced, and the about page explains what this platform does and does not do.