Soil Calculator: Bed and Planter Yardage Over Ohio Clay
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Raised beds go up here in a rush every April, and they go up for a reason: heavy glacial clay holds water long into spring, and building above it is faster than fixing it. That timing is also why the order matters. A bed framed on a Saturday needs filling the same weekend, and the soil calculator is what turns four boards into a number you can buy. The decision underneath the arithmetic is which of three materials is going in, and at what depth each one sits.
Framing in April, Filling Before the Ground Warms
The season sets the sequence. Beds framed while the clay is still saturated can be filled straight away, because nothing has to be compacted and nothing is waiting on the subgrade to dry. What does wait is the clay underneath: breaking up the top inch or two of it before filling lets roots and water cross the join instead of stopping at it, and that job goes better once the ground has drained.
Fall is the quieter half of the year for this work and the better one for improving ground you already have. A couple of inches of blended soil worked into a tired border in October has settled and merged by the time planting starts.
Measuring Inside the Timbers, Not Around Them
A bed is measured on the inside face of the boards. A 4 by 8 foot bed built from 2 by 10 lumber is closer to 3 ft 9 in by 7 ft 9 in of actual soil space, and on a run of six beds that gap is most of a yard.
Depth is the second half of the measurement, and it is decided by the job rather than by the frame:
| What is being filled | Depth to enter |
|---|---|
| Feeding an established bed | 2 to 3 inches, worked into the top 6 |
| New in-ground bed | 6 inches, blended into the native soil |
| Empty raised bed | 12 inches, or to the inside height of the frame |
| Deep planter over 18 inches | the top 8 to 12 inches only, with cheaper fill below |
Running Each Bed as Its Own Area, Up to Five
Rectangle mode takes length and width in feet. Circle mode takes a diameter, which is the mode for a round planter, a ring around a tree or a raised herb barrel. Multiple areas holds up to five footprints in one calculation and adds them. One depth applies to the whole run, so group areas by depth: the beds going in at 12 inches are one calculation and the border at 3 inches is another. Six identical beds can go in as one entry at six times the area.
Depth is entered in inches and accepts 0.25 up to 24. Pick the material next, since each of the three weighs differently and the tons line follows the selection. One optional control adds 5 percent for compaction and spillage. Press calculate and cubic yards, tons and cubic feet come back together, with the option to have them emailed.
Two Thousand, Twenty-Two Hundred, Twenty-Four Hundred
| Material | Pounds per cubic yard | Tons per cubic yard |
|---|---|---|
| Garden Soil, blended with compost | about 2,000 | 1.00 |
| Top Soil, screened | about 2,200 | 1.10 |
| Fill Dirt | about 2,400 | 1.20 |
Garden soil is the lightest because compost is in it, and at 1.00 the tons and the yards read the same, which makes it an easy one to sanity-check. The tools split by job, not by product name. Beds and planters, where things are actually growing, are sized here. Lawn and finish-grading work belongs on the topsoil calculator, and raising ground or filling holes on the dirt calculator. Pick the wrong one and the arithmetic still works; the bed just does not.
Two Raised Boxes, a Deep Planter and a Tired Border
Three examples, all with made-up dimensions.
Two 4 by 10 foot beds filled to 11 inches. Inside area is 40 square feet each, so 80 square feet. Volume is 80 x (11 / 12) = 73.3 cubic feet, which is 73.3 / 27 = 2.72 cubic yards. At 1.00 that is 2.7 tons of garden soil. With the 5 percent box it reads 2.85 yards.
A 3 by 12 foot planter, 24 inches deep, filled in two layers. The bottom 14 inches goes in as fill dirt: 36 x (14 / 12) = 42 cubic feet, 1.56 cubic yards, 1.9 tons. The top 10 inches is garden soil: 36 x (10 / 12) = 30 cubic feet, 1.11 cubic yards, 1.1 tons. Two runs of the tool, two products, and a planter that costs considerably less to fill than one taken to the rim in blend.
A 22 by 4 foot border being fed rather than rebuilt. Area 88 square feet, 3 inches of garden soil tilled into the top 6. Volume is 88 x (3 / 12) = 22 cubic feet, which is 0.81 cubic yards and 0.8 tons. Repeating that for two or three seasons does more for worn ground than replacing it, and it moves a fraction of the material.
The Ten Percent That Disappears in the First Three Weeks
Blended soil settles as the compost in it breaks down and the air works out, typically around 10 percent in the first few weeks and more where a bed is watered hard. Fill above the rim, soak it, and refill once rather than ordering twice.
That settling is separate from the 5 percent box on the form, which covers spillage and what stays in the heap. Both are worth having on a bed order. Have the load tipped onto a tarp, since soil stains a drive and a tarp can be dragged and folded. Delivery is arranged at checkout by ZIP code, and the truck needs clear access to a firm spot to tip on. If mulch is going over the finished beds, size it on the mulch calculator and order the two together.
Common questions
The planter is two feet deep. Does it all have to be garden soil?
No, and it is a waste to fill it that way. Anything below about the top 10 inches is out of reach of most roots, so fill dirt or coarse organic matter that composts in place does the job down there. Run the tool twice, once at the lower depth on fill dirt at 1.20 tons per yard and once at the upper depth on garden soil at 1.00, and order them as two products.
The bed curls around a maple with no straight side to it. What goes in the boxes?
Take the smallest rectangle the bed fits inside and use that, or cut it into two or three rectangles and enter them as separate areas. At bed depths the surplus from squaring off a curve is small, and it gets used along the front edge, which is always where a bed ends up shallowest.
The old beds only dropped a couple of inches. How do I measure a top-up?
Measure down from the inside top of the frame to the soil surface at four or five points and average them. That average is the depth; the inside length and width do not change. Two inches across a 4 by 8 foot bed is 5.3 cubic feet, or 0.2 of a yard, so top-ups are worth combining into one order across every bed you have.
I ran out with one bed still empty. Can I just order the difference?
You can, though a small second delivery for half a yard is rarely worth it. Measure the empty bed, add whatever the filled beds will want after they settle, and order the two together as one figure. Leaving the last bed short and planting it anyway is the more common mistake, and it shows up all season.
How close is the yardage to what the beds actually swallow?
The volume arithmetic is exact. What moves is the material: a blend loses roughly a tenth of its bulk as it settles, a bed dug into native soil takes a little extra where the base was loosened, and some of every load stays in the heap. Order to the calculated figure with the 5 percent on, then expect to top the beds up once after the first hard soaking.
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