Topsoil Calculator

How to use this topsoil calculator

1. Measure the area in feet. If the job covers a few separate patches, add each one. Circles and triangles work for odd corners.
2. Pick the job. The depth fills in from extension guidance: 4 inches for sod or a new lawn over poor soil, 6 inches if you want a full layer of new soil, and 1/2 inch for topdressing. You can type any other depth.
3. For low spots in an existing lawn, enter the average depth of the dips. Lay a straight board across a dip and measure down to the soil at the deepest point. A dip shaped like a shallow dish holds about half as much as a flat-bottomed hole that deep, so enter about half of that measurement.
4. Choose the bag size you’d buy: 0.75 or 1 cubic foot.
5. Under “Settling and prices,” enter what bags and bulk topsoil cost near you and the delivery fee. The numbers there are examples.

How the calculator works

cubic feet   = area × depth ÷ 12
to buy       = cubic feet × 1.10            settling allowance
cubic yards  = cubic feet ÷ 27
bags         = cubic feet ÷ bag size, rounded up
bulk         = cubic yards, rounded up to the next half yard
passes       = depth ÷ 1/2 inch, rounded up  topdressing and low spots

The depths come from three extension services. Rutgers’ sodding guide says that over very poor soil you should spread at least a 4 inch layer of high quality, weed-free topsoil, then till everything you’ve added into the top 6 inches. Illinois Extension sets a goal of 6 inches or more of well prepared soil under a lawn. For topdressing, Clemson Extension says to apply no more than 1/2 inch at a time, because thicker layers can stunt the grass.

The 10% settling allowance is our estimate. Topsoil is sold loose, and it firms up once it’s raked, rolled, and rained on. The Scotts label hints at the same thing: it says a 0.75 cubic foot bag covers 4 square feet at 2 inches, which is only 0.67 cubic feet in place, about 11% less than the bag holds. Set the allowance to 0 if you’re filling to a measured line and plan to top it off later.

We don’t estimate the weight of topsoil. It varies a lot with moisture and soil type, and we couldn’t find a figure we could verify. If you’re hauling it yourself, ask the supplier how much a yard of their soil weighs before you load a pickup.

A worked example

Say you’re laying sod on a 30 × 40 foot backyard where the builder left hard clay, so you plan on 4 inches of new topsoil.

• Area: 30 × 40 = 1,200 square feet
• Volume: 1,200 × 4 ÷ 12 = 400 cubic feet
• With 10% for settling: 440 cubic feet, or 16.3 cubic yards
• Bulk: 16.5 cubic yards at $35, plus $75 delivery, is $652.50
• Bags: 440 ÷ 0.75 = 587 bags, or $2,348 at $4 each

The bulk load costs less than a third as much. At these example prices, bulk always wins once you need more than about 20 cubic feet, which is less than a cubic yard.

In the front yard there are three soft dips that add up to 60 square feet, about 3 inches deep at the center. Entering half the deepest point, 1.5 inches, gives 8.25 cubic feet with settling. That’s 11 bags, a $44 job, spread in 3 passes of 1/2 inch.

Topsoil for common lawn jobs

Each row includes 10% for settling:

Below about a cubic yard, bags are easier to handle and the cost difference is small. Above that, the bag count climbs fast: a 5,000 square foot lawn at 4 inches would take more than 2,400 bags.

Tips for buying and spreading topsoil

• Test your soil before you buy any. Illinois Extension suggests testing during the planning stage, and the results may show that compost worked into the soil you have is enough.
• Mix new topsoil into the soil below instead of leaving it as a separate layer. Rutgers suggests tilling everything you add into at least the top 6 inches.
• Don’t add sand to fix a clay lawn. Illinois Extension says sand isn’t suggested for improving clay soils in home lawns. Use compost or other organic matter instead.
• Grade the finished surface so water runs away from the house. Illinois suggests a slope of 1 to 2 percent, which is about 1/8 to 1/4 inch per foot.
• If tilling leaves the surface fluffy, firm it with a lawn roller before you seed or lay sod. Otherwise it will settle unevenly later.
• Topdress while the grass is actively growing, so it can grow through the new soil quickly.