Soil Calculator for Raised Beds, Planters and Tired Ground

Most raised beds in this state exist because of what is underneath them. A cemented hardpan a few feet down through parts of the Central Valley, heavy clay across the Coast Range valleys and inland basins, fast-draining sand near the shore and in the deserts: in each case the cheapest fix is to build the growing layer above the problem rather than fight it. That decision, how much ground you are building and how deep, is the one this soil calculator prices out in cubic yards. The rest of the page follows the questions in the order they usually arrive.

Do four beds along a fence go in as one entry?

Rectangle takes the inside length and width of a bed in feet, measured inside the timber rather than across it, since the frame itself holds no soil. Circle takes a diameter, which is how a round planter or a tree well goes in. Multiple areas adds up to five pieces at once, so a row of beds along a fence can be entered as a group.

The catch is the depth field: one depth applies to every area in a single calculation. Beds of the same height total neatly; a 12-inch bed and a 24-inch planter are two separate runs, added together afterwards.

How deep does a bed on clay or hardpan really need to be?

Four to six inches is enough to refresh a bed that already has workable soil in it. A new in-ground bed cut into native ground wants about six inches of blended material turned into what is there. An empty raised frame is filled to its full depth, usually 12 inches, and that is the figure that surprises people, because depth moves the order far more than footprint does.

Over hardpan or dense clay, roots are not going any deeper than the bed you build, so 12 inches is a working minimum for vegetables rather than a generous choice. Where a frame stands taller than about 18 inches, there is no sense buying blended soil for the bottom of it. Put fill dirt or coarse organic material in the lower third, keep 8 to 12 inches of garden soil for the rooting layer at the top, and run this calculator twice, once per layer.

What do two beds and a round planter come to?

Worked illustrations, not real orders.

Two 3 by 12 foot beds at 14 inches. Seventy-two square feet of bed: 72 x 14 / 12 = 84 cubic feet, which is 84 / 27 = 3.11 cubic yards. At 1.00 ton a yard for blended soil, that is 3.11 tons.

A 6-foot round planter at 16 inches. A 6-foot circle is 28.3 square feet: 28.3 x 16 / 12 = 37.7 cubic feet, or 1.40 cubic yards.

A 4 by 10 foot frame 24 inches tall, filled in two layers. Forty square feet. The lower 8 inches in fill dirt: 40 x 8 / 12 = 26.7 cubic feet, 0.99 cubic yards, 1.19 tons. The upper 16 inches in garden soil: 40 x 16 / 12 = 53.3 cubic feet, 1.98 cubic yards, 1.98 tons. Two entries, two materials, one delivery.

Why does the soil calculator quote tons for something sold by the yard?

Because the truck is weighed and the bed is not. Volume is the ordering figure for soil here, and the tonnage is there to tell you what is about to land on the driveway. The three materials in the list differ enough to matter: compost-blended garden soil is published on this site at about 2,000 lb per cubic yard, screened topsoil at about 2,200 lb, and fill dirt at about 2,400 lb. That is 1.00, 1.10 and 1.20 tons a yard respectively, so the same 3 yards weighs three tons as a planting blend and three and a half to four as structural fill.

For scale against the shelf, a 40 lb bag holds roughly three quarters of a cubic foot, which puts something in the region of three dozen bags in a single cubic yard, and one modest raised bed past the point where bags make sense.

Is five percent enough when the compost settles?

It is not the same thing, and this is worth being clear about. The optional box on the form adds 5 percent for compaction and spillage, which covers the wheelbarrow and the rake. Compost-rich blends do something separate: they consolidate as the organic fraction breaks down, commonly by 10 to 20 percent over the first few weeks in a new bed.

The way to handle that is not to inflate the depth you enter. Fill slightly proud of the rim, water the bed through thoroughly so it settles on its own schedule rather than yours, and top it up once. Heavily planted beds will ask for an inch or two again each spring, which is normal rather than a sign the order was short.

Which blend goes in a planter, and which belongs under a lawn?

Garden Soil is the blended, compost-rich material for beds, planters and food growing, and it can be planted into as it comes. Work a few inches of it into the native layer at the bottom of an in-ground bed rather than leaving a hard line between imported and existing soil, because roots cross a gradual change far more readily than a sharp one.

Bed work is what this page sizes. Lawn work is the other side of the split: seeding, topdressing and finish grade run on the topsoil tool with Top Soil, which is screened rather than blended. Anything structural, from raising grade to filling holes, is Fill Dirt on the fill dirt tool.

Tired ground rarely needs replacing wholesale. Working two to three inches of blended soil through the top six inches of an existing bed takes a third of the material and a fraction of the lifting, and it is the better answer on clay that holds water too long or on sand that dries out between waterings. Delivery is arranged at checkout by ZIP code, and how a bulk load is scheduled covers the access; ask for the pile on a tarp, since soil marks a driveway and a tarp lets you fold the last of it away. Bark over the finished beds is a separate order on its own tool.

Common questions

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