Topsoil Calculator

Four jobs, four depths that do not mean the same thing

Every published topsoil depth is written for one job, and the four cited here are four kinds of number. A new lawn wants a root zone of at least 4 inches: Michigan State University Extension writes that additional topsoil can be bought when what is there cannot provide an adequate root zone (at least 4 inches) — a total to reach. Top-dressing is the opposite kind of figure: Clemson HGIC caps a pass at no more than ½-inch of material applied at a time, a maximum per application, not a season’s total. A garden bed is a layer added to soil that stays: University of Maryland Extension describes adding 2-4 inches of compost into the top 4 inches, and Clemson allows adding up to 3 inches over an eroded soil. A raised bed is none of those — it is the height of a box you fill, which Utah State University Extension puts at at least 6 to 12 inches for the rooting depth of most vegetables.

The number that costs the most when it travels. Maryland’s 12-24 inches deep for pepper, tomato, and squash is stated for a bed on a hard surface, where the whole depth must be soil. Read as the depth of a raised bed in general it over-orders by up to three times: the same 32 sq ft box is 0.79 cubic yards at 8 in, 1.19 at 12 and 2.37 at 24.

The subtraction nobody does

Only the new-lawn job subtracts, and it is the reason this sheet exists. Pick it and a second field appears for the topsoil already there; the order is the target minus it. Bare subsoil at 4 in: 2.47 cubic yards over 200 sq ft, 67 bags. Two inches already there: 2 in to buy, 1.23 cubic yards, 34 bags — half the delivery, half the spreading. Four inches already there and the sheet orders nothing, and says so. Over 1,000 sq ft the same two inches is the difference between 12.35 and 6.17 cubic yards, or 5 short tons you do not pay to haul and rake. Every other job leaves the depth alone: a pass, a compost layer and a box height are all measured from the surface upwards.

How far a cubic yard goes

Coverage is one division: 27 cubic feet spread at a depth in inches covers 27 ÷ (depth ÷ 12) square feet.

The last column is the 1,000 sq ft lawn used through this sheet. No row is a recommendation: each depth answers the job it was written for.

Bags are sold by volume, not by weight

A sack is printed with its cubic feet — commonly 0.75, 1, 1.5, 2 — while the pound figure moves with how wet the soil was when bagged. The count here therefore comes from volume, and the field opens at 1 cu ft for you to overwrite. The 32 sq ft box at 8 in needs 29 bags of 0.75 cu ft, 22 of 1, 15 of 1.5 or 11 of 2: the same 21.33 cubic feet counted four ways, rounded up because you cannot buy most of a bag. 0.93 cubic yards over a 100 sq ft bed is 25 bags to carry: bulk wins.

Weight, and the two published figures that agree

The order is weighed at 1,620 lb per loose cubic yard, the topsoil row of FHWA Exhibit 5.1 A, footnoted subject to average ±5% variation. Caterpillar’s earthwork table gives 1,600 lb for the same loose material: 1.23 % apart, inside that footnote, so the two agree and this sheet uses the FHWA figure because C-102, the fill dirt calculator, already uses that row — two pages here cannot quote two weights for one yard of soil. Your supplier’s density overrides both. Nothing here is compacted: the exhibit’s embankment column is a highway fill built to a federal specification. Fill below the topsoil, the excavation for it and the swell on a load leaving site are C-102’s work.

Area      A  =  L x W          rectangle
             =  pi x D^2 / 4    circle
             =  b x h / 2       triangle
Buy depth db =  max(0, d - e)  new lawn only
             =  d              every other job
Volume    V  =  A x db / 12    (sq ft, in -> cu ft)
Yards     Y  =  V / 27
Order     Yo =  Y x (1 + a / 100)
Bags      B  =  ceil( Yo x 27 / bag cu ft )
Weight    Wt =  Yo x 1620   (lb per cu yd)
Tons      T  =  Wt / 2000
Cover     C  =  27 / (db / 12)   sq ft per cu yd

Frequently asked

How do I calculate how much topsoil I will need?

Multiply the area by the depth you are actually buying, then divide by 27. The 200 sq ft above at 4 in is 66.67 cubic feet, 2.47 cubic yards. The skipped step is the depth: on a new lawn it is the root zone you want to end up with, so what is already there comes off first.

How many 40 lb bags of topsoil equal a yard?

Read the bag by volume first: a cubic yard is 27 cubic feet, so 27 bags of 1 cu ft, 18 of 1.5, 14 of 2. By weight, at the 1,620 lb per loose cubic yard of FHWA Exhibit 5.1 A, a 40 lb bag is 40.5 to the yard — but only the printed volume is fixed.

How much area will 1 cubic yard of topsoil cover?

27 cubic feet divided by the depth: 648 sq ft at half an inch, 324 at one inch, 108 at three and 81 at the four-inch root zone. The figure is printed beside every result here.

How much topsoil do I need for 2000 square feet?

At a 4 in root zone over bare subsoil, 2,000 sq ft takes 24.69 cubic yards, 40,000 lb or 20 short tons; over 2 in of existing soil it halves. One top-dressing pass at half an inch is 3.09 cubic yards.

How many bags of soil do I need for a 4x8 raised bed?

A 32 sq ft box filled 8 in deep is 21.33 cubic feet: 22 bags of 1 cu ft, 15 of 1.5 or 11 of 2. At 12 in, 32 bags of 1 cu ft. Utah State University Extension puts the box at 6 to 12 inches high.

How many wheelbarrows is 1 yd of topsoil?

27 cubic feet divided by the rated volume of your barrow, stamped on the tray or in its manual. No barrow size ships here: measure yours and divide, as you would read the cubic feet on a bag.

Limits of this sheet

C-105 turns an area, a job and a depth into cubic yards, bags, weight, coverage and a cost, in both unit systems, and exports the takeoff to CSV. It decides no seed or fertiliser rate, reads no soil test, judges no pH, mixes no blend and spaces no planting. The depths are the published ones for the four jobs named; your soil, crop and extension office outrank them.

Sheet C-105 prepared by TakeoffMetric Editorial; no author, credential or field measurement is claimed.