Topsoil Calculator

Volume (yd³) = length (ft) × width (ft) × depth (in) ÷ 12 ÷ 27

L

Length of the bed or lawn, in feet

W

Width of the bed or lawn, in feet

D

Depth of soil to spread, in inches

ρ

Bulk density of the soil, in kilograms per cubic metre

Use it for a raised bed, a new lawn, top dressing an existing one, or filling a low spot. Depth is the figure people get wrong in both directions: four to six inches is a normal cover for a new lawn, eight to twelve for a raised bed, and half an inch is all a top dressing needs. Doubling the depth doubles the order, so it is worth measuring the bed's edges rather than its middle.

1. Top dressing a 10 ft by 10 ft lawn, six inches of topsoil

   1. Area: 10 × 10 = 100 square feet
   2. Depth in feet: 6 ÷ 12 = 0.5 ft
   3. Volume: 100 × 0.5 = 50 cubic feet = 1.85 cubic yards
   4. Topsoil runs about 80 lb per cubic foot: 50 × 80 = 4,000 lb
   5. In metric, 1.85 cubic yards is 1.42 cubic metres, about 1,812 kg

   Two tons of soil is a delivery, not a car boot. The number worth remembering is that one cubic yard covers 100 square feet to a depth of about three inches, so the order here is that figure twice over.

2. A 4 ft by 8 ft raised bed, filled a foot deep with compost

   1. Area: 4 × 8 = 32 square feet
   2. Depth in feet: 12 ÷ 12 = 1 ft
   3. Volume: 32 × 1 = 32 cubic feet = 1.19 cubic yards
   4. Compost is light when it is dry enough to spread: about 45 lb per cubic foot, so 32 × 45 = 1,440 lb
   5. That is 652 kg, roughly a third of what the same volume of topsoil weighs

   The volume is identical to topsoil — 1.19 cubic yards either way — and the weight differs by a factor of nearly three. That gap is why the density row is printed on the result panel instead of being folded silently into the tonnage.

The weight is the weakest figure here, and it is meant to be read that way. Topsoil, garden mix and compost are sold by volume, and their bulk density swings with moisture and organic content: dry compost is around 45 lb per cubic foot and the same compost after a week of rain is nearer 70. Order by the cubic yard and use the weight only to judge whether a delivery can be tipped and wheeled where you want it. Depth is the settled depth, and loose fill settles by 10% to 20% once it is watered in, so a bed built a foot deep and filled to the brim will end up short of it.

How much topsoil do I need for a raised bed?

Multiply the bed's area by the depth you want to fill, in feet, then divide by 27 for cubic yards. A 4 ft by 8 ft bed filled a foot deep is 32 cubic feet, or 1.19 cubic yards. If the bed sits on native ground rather than a hard surface, fill it and let it settle rather than ordering the full depth again next year.

How deep should topsoil be for a new lawn?

Four to six inches of soil for seed to root into, and the soil needs to be firm enough that a heel leaves a dent rather than a hole. A top dressing over an established lawn is much thinner — a quarter to half an inch, worked into the surface — and the same page handles both, because it is the same multiplication.

How much does a yard of topsoil weigh?

About 2,200 pounds, or just under a metric tonne, at the 1,280 kilograms per cubic metre used here. Treat it as a range rather than a figure: soil that has been rained on can be half again as heavy, which is exactly the difference between a delivery you can wheelbarrow and one you cannot.

Is a garden mix the same thing as topsoil?

Not quite. A garden mix is topsoil blended with compost and often a little sand, which makes it lighter, better draining and better for a raised bed where roots have nowhere deeper to go. Plain topsoil is the cheaper fill for leveling ground or topping a lawn. The density difference between them is about 14%, so the weight rows differ even when the volumes match.

How many bags of soil make a cubic yard?

Twenty-seven bags if each one holds a cubic foot, or about 36 of the 40 pound bags sold at a garden centre, which hold roughly three quarters of a cubic foot each. Bagged soil is convenient for a single raised bed and expensive for anything larger — above about two cubic yards a bulk delivery is usually cheaper than the bags.

Will the soil settle after I spread it?

Yes, by 10% to 20% for loose fill, and most of it happens in the first few waterings. Order slightly over rather than exactly at the calculated volume, and if you are filling a raised bed leave the soil an inch below the rim so that rain has somewhere to go.

• Guide for the Use of the International System of Units (SI), NIST Special Publication 811 — the cubic yard and cubic metre factors behind the volume rows — National Institute of Standards and Technology
• The International System of Units (SI) brochure — the kilogram and the tonne, which is what the metric weight row is expressed in — Bureau International des Poids et Mesures (BIPM)