Raised Bed Soil Calculator
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Slope and Terrace Soil Calculator
Average depth across a taper, cubic yards with settle allowance, bags, delivered tons and cost for terracing or filling a slope.
Slope and Terrace Soil Calculator
Chlorova · updated for 2026
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Click “Calculate” to see your results.
Weights and prices are typical landscape-supply midpoints, and every yard varies by moisture, source and screen size, so a wet winter load of topsoil can weigh well past the figure printed here. The average-depth method is exact for a straight taper and approximate for a compound slope, so measure a stepped run as separate strips rather than trusting one depth pair. Settle allowance covers shrink after placement, not compaction under traffic, and a terrace footing of gravel should be tamped in lifts regardless of what the order line suggests. Get the delivery drop site agreed in writing, because a truck that cannot reach your slope tips its load where it can.
Ordering soil for a slope is the landscaping arithmetic that fails twice: depth is never constant across the run, and the volume you measured shrinks once the material settles. A terrace that reads two inches at the top and eight at the toe averages five, and that single average is the whole calculation. This tool converts length, width and a taper into cubic feet and yards, adds a settle allowance, and returns bags, delivered tons and a bill for the delivery day.
Measuring a Taper Before Ordering
- Pick the material, which sets weight, price and shrinkage.
- Measure the length of the slope run being covered.
- Measure the width at right angles to that run.
- Record the thin edge of the taper in inches, not feet.
- Record the deep edge where the toe of the slope sits.
- Add a settle allowance, 10% for soil and 20% for compost.
- Set the bag or barrow volume you actually own.
- Read cubic yards with allowance as the number to order.
- Check delivered tons against what your drive can take.
- Split a long slope into strips and total the volumes.
Average Depth Is the Whole Trick
A taper from two to eight inches is a triangular prism, and its volume equals area times the mean of the two depths, so five inches is the number that matters. Two hundred square feet at five inches is 200 times 5 twelfths, or 83 cubic feet, which divides to 3.09 cubic yards in place.
Settle allowance multiplies that figure rather than the depth, because shrink happens to the pile you order, not the pile that ends up on the slope: ten percent turns 3.09 into 3.40 cubic yards to buy. Weight follows from a per-yard density, 2,400 lb for topsoil, so the load lands near 4.1 tons. Cost is ordered yards times price plus a flat delivery charge, which is why a small job carries a stubbornly large per-yard unit price.
Worked Example: A Twenty-Foot Terrace Run
- Choose screened topsoil for a run 20 ft long and 10 ft wide.
- The taper reads 2 in at the top and 8 in at the toe.
- Area is 20 times 10, so 200 sq ft to cover.
- Average depth prints five inches, the key figure here.
- Volume in place comes out near 83 cubic feet.
- Divided by 27, that is 3.09 cubic yards placed.
- A 10% settle allowance makes the order 3.40 yards.
- In 1.5-cu ft barrow loads, that is 62 trips.
- Each bag covers only 3.6 sq ft at five inches deep.
- Weight arrives at 4.07 tons of damp soil.
- Cost reads $193.83 delivered, material price plus the fee.
- The handling line says heavy barrow work or a tipper.
Weights, Prices and Shrink by Material
Typical landscape-yard figures for screened bulk material delivered in moderate quantity. Pounds per cubic yard drive the tonnage line, and the shrink column is the settle allowance this calculator applies to your order volume rather than to the depth you measured.
| Material | lb per cu yd | Typical $/cu yd | Settle allowance | Best used as |
|---|---|---|---|---|
| Sand | 3000 | 28 | 5% | Drainage layer |
| Crushed gravel | 2900 | 30 | 5% | Terrace footing |
| Topsoil | 2400 | 35 | 10% | Planting fill |
| Raised-bed mix | 1500 | 55 | 8% | Deep bed lift |
| Compost | 1000 | 45 | 20% | Thin soil amendment |
| Bulk mulch | 500 | 40 | 15% | Surface cap |
Key Terms
- Toe of slope
- The low edge of a bank, where fill runs deepest and water collects.
- Settle allowance
- Extra volume ordered to cover shrinkage after material is placed.
- Lift
- One layer of fill placed and firmed, rather than the whole depth at once.
- Road base
- Crushed aggregate compacted to a stable, draining substrate under hard surfaces.
- Trimmed level
- The finished surface height a terrace is filled up to.
- Tipper load
- A small truckload delivered and discharged where the vehicle can reach.
The Parts That Go Wrong on a Slope
- Never bury a taper in one deep pour on a bank, because backfill that thick slumps toward the toe and cracks the finished surface two seasons later; place it in lifts and firm each one.
- The thin edge shrinks out of existence first, so order against the average depth but check the taper again after settling and top up the shallow end rather than the whole run.
- Water or rain before planting pre-shrinks topsoil better than any allowance you can type in, which is why experienced crews fill, soak, wait a week and then trim to level.
- Delivery cost dominates small jobs, and a two-yard order of $35 soil is really a $75 truck decision, so compare per-yard totals after delivery rather than the headline price.
- Weights are the hidden constraint on a raised terrace, since three yards of wet gravel on a timber-boxed bench is over four tons pressing on joints that were built for soil.
Common Mistakes & Fixes
- Ordering against the deepest measurement on the slope and paying good money for air.
- Averaging two depths that sit on a compound, stepped slope.
- Forgetting shrink and finding the thin edge bare by spring.
- Using pure compost as a deep fill that then drops six inches.
- Ignoring the delivered tonnage until a loaded truck cannot reach the slope at all.
- Compacting gravel in one pour instead of in tamped lifts.
- Buying bagged soil at the store for a load-sized job.
When to Use This Calculator
Reach for it whenever a fill depth changes across a run: terracing a bank, cutting steps into a slope, building drainage backfill behind a retaining wall, or lifting beds along a gradient. For a level bed of uniform depth, the raised-bed soil and bulk bagged material tools are the quicker paths, and the mulch depth calculator handles a flat top-dressing. Use this one the moment you have a thin edge and a deep edge to reconcile.
Slope and Terrace Soil Calculator: Frequently Asked Questions
How do I calculate soil needed for a sloped area?
Multiply length by width to get area, then multiply by the average of the shallow and deep depths. Convert cubic feet to cubic yards by dividing by 27, and add your settle allowance to that figure before ordering, since the pile shrinks after placement.
How much extra should I order for settling?
About 5% for sand and crushed gravel, which compact rather than shrink, and 10% for topsoil. Compost and mulch lose the most volume, so allow 15 to 20%, and a raised-bed blend sits in between at roughly 8%.
How heavy is a cubic yard of topsoil?
Screened topsoil runs near 2,400 lb per cubic yard when dry, and wet material can push past 3,000. That is why the tonnage line matters on a slope: three yards is over four tons, and it arrives in one drop that you cannot easily move again.
Is it cheaper to buy bulk or bagged soil?
Bulk wins once you need more than about two cubic yards, because a bagged 1.5 cu ft load costs several times the delivered per-yard rate. Below that, and where a truck cannot reach, bags or a trailer pickup are usually the sensible answer despite the unit price.
Can I use this for a retaining wall backfill?
Yes, treat the backfill as a strip whose length runs along the wall and whose taper follows the drainage layer. Gravel is the right material selection there, and remember to compact it in lifts rather than pouring the full depth behind the wall at once.
Why does my finished terrace look thinner than I ordered?
Because the volume figure was measured loose in the truck and then consolidated under rain and foot traffic, which is exactly what the settle allowance is meant to cover. Order with the allowance, soak the fill before planting and top up the shallow end rather than re-buying the whole run.
What depth is too deep to fill in one pass?
On a slope, keep each lift under roughly four inches of soil and firm it before the next, since deep unbonded fill creeps downward and cracks. A foot of fresh soil on a bank is better placed over several days than in one afternoon.
Sources & Further Reading
- Estimating Soil, Mulch and Water Needs for Landscape Planting — University of Florida IFAS Extension. Basis for volume and settle-allowance method.
- Soil and Compost Buying Guides for Home Landscapes — Iowa State University Extension and Outreach. Supports per-yard weights and bulk versus bagged pricing.
- Terrace and Slope Stabilization Practice Standard — USDA Natural Resources Conservation Service. Source of lift placement and compaction guidance on fills.
Chlorova Gardening Team
Builds, checks and documents every tool we publish
Chlorova editorial review
Checked against extension-service publications
Formula verified against published references · Updated
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