Soil Calculator for Raised Beds Built on Stony Till
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Most raised beds in this state exist because the ground underneath them is stony glacial till with ledge not far below, and nobody wants to fight that with a fork. What this soil calculator mostly has to correct is how much a box that size actually swallows.
A bed 4 feet by 12, filled a foot deep, holds 48 cubic feet. That is 1.78 cubic yards, or roughly 64 bags at 40 lb apiece. People arrive here planning on a dozen.
Three beds and a planter: does the soil calculator take them all?
It does. Multiple areas totals up to five separate pieces into one figure, which is what you want before booking a single delivery.
Measure inside the boards, in feet. The frame itself has real thickness, and on a small box it is enough to matter.
Round planters and half barrels go in as circles, diameter straight across the inside.
A ground-level bed with a curved front gets the rectangle that the curve mostly sits inside. Soil is forgiving that way; you will be moving the last wheelbarrow by eye regardless.
Twelve inches of blend, or four of fill and eight of blend?
Depth is where the money is, and a tall box does not need planting mix all the way to the bottom.
Roots live in the top 8 to 12 inches. Below that, anything stable will do: fill dirt, or coarse organic matter that will break down in place.
| Bed | Depth to enter |
|---|---|
| Amending an established bed | 2 to 3 inches, forked through the top 6 |
| New ground-level bed | 6 inches |
| Raised box, root zone | 8 to 12 inches of blend |
| Anything below that in a tall box | fill, run as its own calculation |
Hypothetical. Two boxes at 4 by 10 and one at 4 by 6, all 12 inches deep.
- 40 + 40 + 24 = 104 sq ft
- Filled solid: 104 cu ft, which is 3.85 cu yd
- Bottom 4 inches as fill: 104 x 0.333 = 34.67 cu ft, 1.28 cu yd, 1.54 tons
- Top 8 inches as blend: 104 x 0.667 = 69.33 cu ft, 2.57 cu yd, 2.57 tons
Two runs of the tool, two materials, one delivery day. The lower layer costs less and grows the same tomatoes.
Why does the ton figure move when I change the dropdown?
Because the three ground materials do not weigh the same, and the tool uses the weight of whatever is selected.
| Material | Per cubic yard | Tons per yard |
|---|---|---|
| Garden soil, blended | about 2,000 lb | 1.00 |
| Screened topsoil | about 2,200 lb | 1.10 |
| Fill dirt | about 2,400 lb | 1.20 |
So pick the material before you read the tonnage, not after.
Cubic yards = area sq ft x depth in, divided by 12, divided by 27. Tons = cubic yards times the figure in the right-hand column. Garden soil is the easy one: yards and tons come out at the same number.
The rest of the form is quick. Rectangle, circle or multiple areas. Feet for length, width and diameter. Inches for depth, from 0.25 to 24. Results as cubic yards, tons and cubic feet, with Email my quote if you want them in writing.
Do I tick the 5%, or let the bed settle and top it up?
The box adds 5% for compaction and spillage. On beds, tick it and expect to come back anyway.
Blended soil carries a lot of organic matter, and organic matter shrinks. A newly filled box can drop a tenth of its depth in the first few weeks as the compost consolidates, and more than that over a season of heavy planting.
So fill slightly above the rim, water it in properly, and top it off once. Then plan on an inch or two every spring in the beds that work hardest.
Put the pile on a tarp if it is landing on anything you care about. Soil stains concrete, and dragging the tarp beats sweeping.
Timing helps more than the allowance does. Beds filled once the ground has dried out in spring have a few weeks to consolidate before anything is planted into them, and the topping-off happens while the box is still empty and easy to reach. Filling a box the same afternoon you want to plant it means doing the same job twice, the second time around the seedlings.
Is this a box job or a lawn job?
The tools split by job rather than by product name, and the three materials are not interchangeable.
Garden soil is topsoil blended with compost, ready to plant into. Vegetable boxes, flower beds, planters. That is what this page sizes.
Screened loam, sold here as Top Soil, is the natural surface layer run through a screen to take out the rock and roots that till is full of. Lawns and finish grading, sized on the loam calculator.
Fill dirt is subsoil. Structure only, no planting. Raising a grade, closing a hole, the bottom of a deep box. It has its own fill calculator.
Where the ground is simply tired rather than impossible, the cheaper move is to fork 2 to 3 inches of blend through the top 6 rather than replace the lot. A third of the material, a third of the work, and roots get into the native soil sooner. Full replacement is for ground spoiled by construction debris.
With the yardage settled, open the product page, set a quantity and a date, and delivery is arranged at checkout by ZIP code. The truck needs firm ground and clear room to tip, which the delivery page sets out.
Common questions
Is 5% enough allowance when the blend is going to settle?
No, and it is not meant to be. The box covers handling and spillage on the way in. Settling is a separate matter: allow a tenth on top for a freshly filled box, fill proud of the rim, water it, and top off once it has dropped.
The bed sits on ground that slopes. What depth do I enter?
The average depth of soil inside the box, measured from the growing surface down. On a slope the uphill wall is shallower than the downhill one, so measure at both ends and take the mean. For a ground-level bed on a grade, split it into two areas and average each separately.
My bed goes round a corner in an L. Do I measure it as one shape?
Split it. Two rectangles in multiple areas, entered so they do not overlap where they meet. The tool adds them. Measuring an L as one big rectangle buys soil for a corner that is still lawn.
Does the area include the boards?
It should not. Measure the inside faces. On a 4 by 10 box, two inch boards cost you better than three cubic feet of capacity, and four boxes measured outside the frame add up to most of a half yard.
Can the fill and the blend come on one order?
Run the tool twice and order both, yes. Ask for two tipping spots if there is room, because mixing the piles defeats the point of layering them. If there is only one clear spot, take the fill first, get it in the boxes, then bring the blend.
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