🌱 Topsoil Calculator

How to Calculate Topsoil

Topsoil is sold by the cubic yard in bulk and by the cubic foot in bags, but you measure the job in square feet and inches. One divisor bridges the gap.

The 324 comes from 27 cubic feet in a cubic yard times 12 inches in a foot. Memorise the consequence instead of the arithmetic: one cubic yard covers 324 sq ft at 1 inch deep, 108 sq ft at 3 inches, and 81 sq ft at 4 inches.

Add 10 to 15% for settling. Loose delivered soil is full of air. Once it is spread, watered and walked on it loses roughly a tenth of its volume, and a bed filled exactly to the rim on delivery day sits an inch low a month later. The calculator adds 10% by default.

Working out an irregular lawn or bed shape? Break it into rectangles and circles with our square footage calculator first.

How Deep Does Topsoil Need to Be?

Depth is where most topsoil orders go wrong — usually far too shallow for planting and far too deep for a lawn. Grass roots and vegetable roots want very different things.

The 1/4 inch rule for lawns

Topdressing a lawn means applying a thin layer of soil or compost over living grass. A quarter inch is the maximum in a single pass, and half an inch is the absolute ceiling on a thin, rough lawn. Any deeper and you smother the crowns — the grass yellows within a week and dies in patches.

If a low spot needs two inches of fill, it needs three or four applications a season apart, or you strip the sod, fill, and re-lay it. There is no shortcut, and burying a lawn in an inch of topsoil is the fastest way to have to reseed the whole thing.

Never pile soil against tree trunks or over root flares. More than an inch or two of added soil over a mature tree's root zone suffocates the fine feeder roots that live in the top 12 inches, and the tree can take years to visibly decline.

Topsoil, Garden Soil, Compost and Fill Dirt Are Not the Same Thing

These get used interchangeably at the yard counter and they should not be. Buying the wrong one costs either money or a season.

Compost is not soil. Beds filled with straight compost hold too much water, shrink dramatically as they finish decomposing, and run nutrient levels high enough to burn seedlings. Compost is 20 to 30% of a good bed mix, not 100%.

Fill dirt is not topsoil. It is subsoil with the organic content removed or never present. It is the right and cheap answer for raising a grade under a patio or filling a pool excavation, and the wrong answer for anything you intend to grow in.

Ask two questions when ordering bulk: is it screened, and what is it screened to? A half-inch screen gives soil clean enough to rake smooth. Unscreened topsoil at half the price will cost you the difference in hours picking rocks out of it.

Filling Raised Beds Without Overpaying

Raised beds swallow far more soil than people expect. A standard 4 × 8 ft bed at 11 inches of fill is 29 cubic feet — about 1.1 cubic yards, or 40 bags of 0.75 cu ft topsoil. Three of those beds is over 3 cubic yards, which is a bulk delivery, not a trip to the garden centre.

A mix that actually works

Straight topsoil in a raised bed compacts into a brick. Straight compost shrinks by a third in one season. The blend the calculator suggests is:

• 60% screened topsoil or garden mix — the mineral body that holds structure and nutrients.
• 30% compost — organic matter, biology and water-holding capacity.
• 10% aeration — coarse perlite, pumice, or fine bark. Not fine sand, which turns loam into something closer to concrete; if you do use sand, it has to be coarse washed sand, and our sand calculator covers the grades.

Topping up an existing bed each spring is normal — expect to add 1 to 2 inches a year as the organic fraction finishes breaking down. That is the bed working, not a mistake.

Filling the bottom with wood or brush

You will read a lot of advice about filling the lower third of a deep bed with logs, branches or leaves to save on soil. It genuinely works in a bed 18 inches or deeper, and it genuinely saves money. Be honest with yourself about the trade: the fill decomposes and the bed level drops several inches over two or three years, and while it is breaking down it ties up nitrogen right where your roots are.

Do it in tall beds where you are never planting below 12 inches, keep the wood well clear of the root zone, and plan on topping up. Do not do it in a 10 or 12 inch bed — there is no room to lose.

Do not line the bottom with plastic. Beds need to drain into the ground below. Cardboard or a permeable weed barrier over grass is fine; sheet plastic makes a planter with no drainage holes.

How to Topdress a Lawn

1. Mow shorter than usual, about a third lower, and bag the clippings so the soil reaches the surface rather than sitting on thatch.
2. Core aerate first if the lawn is compacted or has more than half an inch of thatch. Topdressing over a plugged lawn puts the new soil down into the root zone where it does something, rather than sitting on top.
3. Overseed now if you are going to, before the soil goes down, so seed lands in the aeration holes.
4. Spread no more than 1/4 inch — 0.8 cubic yards per 1,000 sq ft. Dump small piles and spread from them rather than trying to spread from one big heap.
5. Work it in with the back of a landscape rake or a levelling lute until the grass blades are visible through the soil everywhere. If any patch is buried, move soil off it now.
6. Water lightly to settle the material into the canopy and around the crowns.
7. Repeat once or twice a season for low spots rather than trying to fix them in one pass.

Mistakes to Avoid

• Burying the grass. Anything over half an inch kills the crowns. Quarter inch, every time.
• Topdressing with a different soil texture than the lawn already has. A layer of sand over clay, or clay over sand, creates an interface roots refuse to cross.
• Ordering by weight when you measured by volume. A cubic yard of dry screened topsoil is about 1.1 tons; wet or clay-heavy soil is 1.4 tons or more for the same volume.
• Buying bags for a bulk job. 36 bags of 0.75 cu ft make one cubic yard, at roughly triple the delivered bulk price.
• Overloading a pickup. A cubic yard of moist topsoil weighs 2,600 lb — more than the payload of most half-ton trucks. Half a yard per trip is the honest limit.
• Spreading soil over a wet lawn or wet bed. You will compact everything you walk on and undo the point of the exercise.

Mulching the beds afterwards? Our mulch calculator covers depth and bag counts, and the sod calculator handles rolls and pallets if you are turfing over the finished grade. If you are stripping topsoil rather than adding it — every patio excavation starts that way — the paver calculator works out the base and bedding that replaces it.

Bulk or Bagged, and What It Weighs

The breakpoint is roughly one cubic yard. Below that, bags are more convenient and the price difference is small. Above it, bulk wins by a wide margin and the gap grows fast.

Bulk delivery fees run $50 to $150 depending on distance and truck size, and most yards have a minimum load. That fee is why one cubic yard is the breakpoint rather than half a yard — under a yard, the delivery costs more than the soil.

Weight, trucks and access

• Dry screened topsoil: about 2,200 lb per cubic yard (1.1 tons).
• Moist screened topsoil: about 2,600 lb per cubic yard (1.3 tons).
• Wet or clay-heavy soil: 2,800 lb or more per cubic yard (1.4 tons+).
• Compost: 1,000 to 1,400 lb per cubic yard — roughly half the weight of soil for the same volume.

Rain before delivery can move the weight of a load by 20%, which matters if you are being sold by the ton rather than the yard. Buy soil by volume where you can, and if a supplier only quotes tons, ask what moisture assumption sits behind the conversion.

Plan the drop point before the truck arrives. A cubic yard of soil is a heap about 5 ft across and 3 ft high, and it will kill the grass under it within two or three days. Tarp the driveway instead — moving a yard by wheelbarrow is roughly 9 loads in a 6 cu ft barrow, and you will not finish 6 yards in an afternoon.

Frequently Asked Questions

How much topsoil do I need?

Multiply the area in square feet by the depth in inches and divide by 324 for cubic yards. A 600 sq ft area at 4 inches deep is 7.4 cubic yards, or about 8.1 with a 10% settling allowance. One cubic yard covers 324 sq ft at 1 inch and 81 sq ft at 4 inches.

How much does a cubic yard of topsoil weigh?

About 2,200 lb (1.1 tons) dry and screened, around 2,600 lb (1.3 tons) moist, and 2,800 lb or more if it is wet or clay-heavy. Moisture changes the weight far more than soil type does, which is why buying by volume is safer than buying by the ton.

How many bags of topsoil are in a cubic yard?

36 bags of 0.75 cu ft — the standard 40 lb topsoil bag. It is 27 bags at 1 cu ft, 18 at 1.5 cu ft, and 13.5 at 2 cu ft. At typical bag prices that works out to two or three times the delivered bulk price, so anything over about a cubic yard should be ordered loose.

How deep should topsoil be for a new lawn?

4 to 6 inches of good soil over loosened subsoil. Below 4 inches the roots hit compacted subsoil and the lawn browns out in the first dry spell. Loosen the subsoil before spreading so there is no hard interface for roots to stop at.

How much topsoil do I need to level a lawn?

Only 1/4 inch per application, which is 0.8 cubic yards per 1,000 sq ft. A half inch is the absolute maximum on a rough lawn. Deeper than that smothers the grass crowns and kills it in patches. Fix a two-inch low spot over several seasons, or lift the sod, fill, and re-lay it.

How much soil does a 4x8 raised bed need?

A 4 × 8 ft bed filled 11 inches deep is 29.3 cubic feet, or about 1.1 cubic yards — 40 bags of 0.75 cu ft, or 15 bags of 2 cu ft. At 6 inches of fill it is 16 cubic feet. Fill to about an inch below the rim so watering does not wash soil over the side.

What is the best soil mix for a raised bed?

About 60% screened topsoil or garden mix, 30% compost, and 10% aeration such as coarse perlite, pumice or fine bark. Straight topsoil compacts into a brick; straight compost shrinks by a third in a season and can burn seedlings. Do not use fine sand as the aeration component in a loam soil.

What is the difference between topsoil and garden soil?

Topsoil is native soil that has been screened to remove rock and debris — a bulk material for grading, lawns and filling. Garden soil is topsoil already blended with compost and often sand, sold in bags at two to three times the price. For anything over a cubic yard, buy bulk topsoil and add your own compost.

Can I use compost instead of topsoil?

Not on its own. Compost holds too much water, shrinks noticeably as it finishes decomposing, and can run nutrient levels high enough to burn seedlings. It should be 20 to 30% of a bed mix, not the whole thing. As a thin topdressing over an existing lawn or bed, it is excellent.

What is the difference between topsoil and fill dirt?

Fill dirt is subsoil with little or no organic content. It is cheap ($5 to $20 a yard against $18 to $45), it compacts well, and it is the right material for raising a grade under a patio or filling a hole. Nothing grows well in it. Use fill dirt for the bulk of a deep fill and cap it with 4 to 6 inches of topsoil.

How much extra topsoil should I order for settling?

10 to 15%. Delivered soil is loose and full of air; once spread, watered and walked on it loses roughly a tenth of its volume. Raised beds settle at the high end of that range because of the organic fraction, and will need topping up by an inch or two every spring regardless.

How much topsoil fits in a pickup truck?

By weight, not by volume — that is the limit that matters. A cubic yard of moist topsoil weighs about 2,600 lb, more than the payload of most half-ton pickups. Half a cubic yard per trip is the honest figure for a half-ton truck, and about one yard for a three-quarter-ton.

Should I put topsoil over grass?

Only in a thin topdressing of 1/4 inch or less, and only if you want to keep that grass. Burying an existing lawn under 2 or 3 inches of soil to start over does not work well — the dead thatch layer underneath becomes an interface roots will not cross. Kill or strip the old lawn first, then bring in soil.

Can I put topsoil around a tree?

No more than an inch or two, and never against the trunk or over the root flare. A mature tree’s feeder roots live in the top 12 inches of soil and need air. Adding several inches of soil over the root zone suffocates them, and the decline often takes two or three years to become visible — long after anyone connects it to the cause.