Soil Calculator: Filling Beds on Ground That Drains Straight Through
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The commonest way a bed order goes wrong here is a scatter of bags over native sand and a hope that it will hold together. It does not: water and nutrients run past the root zone within a day or two of a downpour, and by the second season the bed has thinned back to what was there before. This soil calculator sizes the alternative, which is a real depth of blended material either boxed in above the ground or worked properly into it. Depth is the field that decides the order, and on sand it wants to be honest.
Sand that drains through, and the depth a bed needs because of it
An in-ground bed cut into deep sand needs the blend mixed down into the top six inches rather than laid in a shallow skin on the surface. A thin imported layer sitting on loose sand behaves like a saucer with no bottom: the water leaves through the base and the roots follow it down into ground that holds nothing.
A raised box gets around that by carrying its own volume. Twelve inches of blend in an empty frame is the working figure, which is more than most people picture and is where the bag-counting usually falls apart. An in-ground bed being cut fresh takes about six inches. A bed that is simply tired and low takes four to six, or two to three inches worked through the existing soil if the intention is feeding rather than filling.
On a flatwoods lot that sits wet for part of the year there is a second reason to build up rather than dig down. Beds here go up because the water table comes up, and a boxed bed keeps roots above the level a heavy August week brings the ground to.
Beds, a planter and a palm ring in one pass of the soil calculator
Rectangle takes a length and a width in feet. Circle takes a single diameter in feet, which handles a half barrel, a round planter or a ring cut around a palm. Multiple areas totals up to five pieces in one calculation, so four boxes along a fence do not need four separate runs.
Depth is in inches and runs from a quarter inch to 24, and one depth applies to everything in the run. That ceiling is worth knowing before you start: a box standing taller than two feet has to be entered as two runs regardless, which suits it, because a deep box should not be filled with blend all the way to the bottom anyway.
The material line sets the weight behind the tons reading. The checkbox adds an optional 5 percent for compaction and spillage. The panel returns cubic yards, tons and cubic feet at once, with a button to email the figure to yourself.
The lightest yard on the truck, and why beds still get ordered by volume
Cubic feet is the footprint in square feet times the depth in inches, divided by 12. Cubic yards divides that by 27, a yard being a three-foot cube, and that is the unit beds are planned and bulk soil is loaded in. Tons converts that volume using the published weight of the material selected.
A blended garden soil is the lightest thing on the list at about 2,000 lb a cubic yard, which works out at an even 1.00 ton, so the two readings land on the same number and people assume the tool has repeated itself. It has not. Screened topsoil is heavier at roughly 2,200 lb, or 1.10 tons, and fill dirt heavier again at about 2,400 lb, or 1.20 tons, so the same box priced in the wrong material comes back with the wrong weight on the ticket.
Two 4 by 10 boxes, a 30-inch planter and a border that just needs feeding
Hypothetical beds, worked longhand.
Two boxes, each 4 by 10 feet, filled to 11 inches. Together that is 80 square feet. 80 x 11 = 880, divided by 12 is 73.33 cubic feet, divided by 27 gives 2.72 cubic yards, which at 1.00 ton to the yard is 2.72 tons. With the 5 percent ticked, about 2.85 of each.
The planter is 3 by 6 feet and stands 30 inches, so it goes through twice. The bottom 12 inches takes structural material: 18 square feet x 12 = 216, divided by 12 is 18 cubic feet, divided by 27 is 0.67 cubic yards, or 0.80 tons of fill dirt at 1.20. The top 18 inches is where roots live: 18 x 18 = 324, divided by 12 is 27 cubic feet, divided by 27 is exactly 1.00 cubic yard, or 1.00 ton of blend. Paying for a blend at the bottom of a knee-high box buys depth nothing ever reaches.
The tired border along the drive is 60 square feet and wants 3 inches worked into the existing soil: 60 x 3 = 180, divided by 12 is 15 cubic feet, divided by 27 is 0.56 cubic yards, or 0.56 tons. Small orders like that are worth adding to a bigger delivery rather than chasing on their own.
Filling proud, because a compost blend keeps dropping
A blend with compost in it consolidates as the organic fraction breaks down and the material takes its first real watering. Fill above the rim, water it in properly rather than treading it down, and expect to come back with a wheelbarrow load two or three weeks later. Doing that once at the start beats topping up every spring.
The 5 percent option covers spillage and the handling losses between the pile and the bed. It is not a settling allowance, so on new boxes order to the upper end of your figure. Have the load tipped onto a tarp if it is landing on a drive, since soil stains concrete and a tarp turns the cleanup into a drag and a fold.
Where this page stops and the fill order starts
Three products sit behind the material line and each one has its own job. Garden Soil is the blend this page is built around: raised beds, planters, planting holes and borders. Top Soil is the screened growing layer for lawns and finish grading, sized on the topsoil calculator. Fill Dirt is the structural material for raising ground and filling hollows, sized on the dirt calculator.
Where a bed area has to come up in level first, bring the fill to within four to six inches of your finished grade, then switch tools and order the growing layer as a second line. Two numbers, two products, one delivery. Set the quantity and a date on the listing; delivery is arranged at checkout by ZIP code, and how a delivery is arranged covers the access. Bed mulch on top is sized separately once the beds are filled.
Common questions
The front border is a long curve that follows the drive. What length and width do I type?
Treat it as straight pieces. Take the length along the middle of the curve rather than the inside or outside edge, use an average width, and if it swings a long way, split it into two or three rectangles under Multiple areas. A border that is over by a wheelbarrow load is no problem; one that is short leaves a bare stretch at the far end.
The boxes dropped a couple of inches over the wet season. Do I measure the gap or the whole box?
The gap. Rest a straightedge across the frame, measure down to the soil at a few points, and enter the average as your depth with the full footprint of the box. Entering the full frame depth on a box that is already three quarters full is the most expensive mistake on this page.
Half a yard out with the last box empty. Order again, or wait?
Usually it is worth adding to something else rather than moving on its own. Fill what you have, plant what is finished, and hold the last box until you have another reason to order. A part-filled box left through a wet spell does no harm.
How close is the yardage on beds I measured to the nearest inch?
Close. The arithmetic is exact and a frame gives you honest measurements, so the only real variable is settling. An in-ground bed is looser, because the boundary between imported blend and native sand is not a clean line, and there you should treat the figure as a good starting quantity.
Which of the three soils do I actually put in the cart once I have the yardage?
Garden Soil for anything you are planting into. Top Soil where grass is going on top. Fill Dirt for the part of the job that is purely about bringing a level up. If a single bed needs two of those, run the calculator once for each layer and order them as separate lines so they arrive as separate piles.
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