How much soil mix for your bed — cubic yards, bags & mix split
Enter the diameter across the top — the tool halves it to the radius.
Fill depth is how deep you actually add soil — most growers fill 6–12 in and may bottom-fill the rest (logs, cardboard). This is the single biggest driver of how much you buy. Always use INTERIOR measurements.
Fresh mixes settle 10–20% in the first season. Default 15% suits a blended garden mix; use ~5–10% for pre-compressed bagged mix, ~15–20% for lightweight/soilless.
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Raised Garden Bed Soil Calculator — guide & how to use
Planning estimate, not a guaranteed quantity. Order quantities vary in practice — buy slightly over rather than under, since running one bag short mid-project costs more than one spare bag. Volumes assume the bed is filled solid to the stated depth; bottom-filling (logs, cardboard, gravel) reduces what you actually need. All math runs privately in your browser.
What it does
This calculator turns your bed dimensions and fill depth into the
soil volume you need — in cubic feet and cubic yards — then converts it to a real
bag count at your chosen bag size. It also splits the total into
topsoil, compost, and aeration by your chosen recipe (each with its own bag count),
adds a settling buffer so the bed doesn't finish short, and can compare
bag vs bulk cost if you enter prices.
How to use it
Pick the bed shape (rectangular, or round/cylindrical for pots and stock tanks).
Enter the interior length & width (or diameter), each with its own unit, plus the fill depth.
Set the number of identical beds, choose a mix recipe, and adjust the settling buffer.
Pick your bag size, optionally add prices, and read the total volume, bag count, and mix breakdown.
How the math works
Unit normalization: every length is converted to feet first — in ÷ 12, cm ÷ 30.48. All volume math is done in cubic feet.
Base volume: rectangular = L × W × depth; round = π × radius² × depth, where radius = diameter ÷ 2.
Multiple beds: base volume × quantity (integer ≥ 1).
Mix split: each component = ordered volume × its % (the three must sum to 100).
Bag count = ceil(volume ÷ bag size) — always rounded UP, since you can't buy a partial bag. Per-component counts are each rounded up independently, so they can total one more than the simple bag count.
Bulk nudge: at ~14 cu ft (≈½ cu yd, ≈9 bags @ 1.5 cu ft) bulk is usually cheaper; if both prices are entered the tool states the dollar difference.
Worked example
A 4 ft × 8 ft bed, 10 in fill depth, 1 bed,
60/30/10 recipe, 15% settling, 1.5 cu ft bags:
Depth 10 in → 0.833 ft. Base = 8 × 4 × 0.833 = 26.7 cu ft.
+15% settling → 30.7 cu ft ordered (≈ 1.14 cu yd).
Bags = ceil(30.7 ÷ 1.5) = ≈ 21 bags.
Mix split: topsoil 60% = 18.4 cu ft (13 bags), compost 30% = 9.2 cu ft (7 bags), aeration 10% = 3.1 cu ft (3 bags).
Component bags each round up, so they total 23 here vs the simple 21 — buy the per-component counts as your shopping list.
At ~31 cu ft you're well past the ~14 cu ft bulk threshold, so the tool nudges you to price-check bulk delivery (≈1.14 cu yd).
Internal math keeps full precision; volumes display to 2 decimals, bag counts use ceil (round up), and currency to the cent — so hand math may differ by a fraction.
Accuracy notes & assumptions
This is a planning estimate, not a guaranteed quantity. Buy slightly over rather than under — running short mid-project is costlier than one spare bag. Keep 1–2 spare bags for first-season top-up.
Fill depth, not wall height, drives the number. Bottom-filling techniques (hügelkultur logs, cardboard, inverted pots, drainage gravel) reduce actual soil needed — subtract that filled depth from your fill depth.
Settling is real and variable: lightweight/soilless mixes settle ~15–20%, blended garden mixes ~10–15%, pre-compressed bagged mixes ~5–10%. The default 15% is a middle-of-road blended-mix figure.
Bag cubic-footage is nominal. Compressed/dehydrated bags (coir, some compost) expand when wetted and yield MORE than the printed volume; loose-filled bags may yield slightly less.
Recipe presets are common starting points, not soil-science gospel. Ideal mix varies by crop, climate, and drainage. "Aeration" = perlite, vermiculite, pumice, or coarse sand — these are not interchangeable by performance even when the volume math is identical.
Bulk-vs-bag thresholds and prices are regional and time-sensitive. The ~14 cu ft / 9+ bag rule and $40–80/cu yd bulk figures are US 2025–2026 ballparks for delivered raised-bed mix — verify locally.
Round-bed volume uses a true cylinder. Tapered pots (wider at top) hold LESS than the cylinder estimate, so for steeply tapered planters the result is a slight over-estimate — a safe direction.
Dry-quart and liter conversions are label-matching convenience only; bag labels round (a "50 dry quart" bag is ~1.94 cu ft, close to but not exactly 2 cu ft).
Common mistakes this avoids
Measuring the OUTSIDE of the frame instead of the inside soil cavity — inflates volume by the wall thickness on all sides.
Using wall height as fill depth — most beds aren't filled to the brim, and many are bottom-filled, so this overbuys dramatically.
Forgetting the settling buffer entirely — the bed finishes 2–4 inches low after the first watering/season.
Filling a deep bed with 100% compost (slumps, can burn roots) or 100% topsoil (compacts) — the mix split exists to prevent this.
Rounding bag count down — it's ceil, not round; 9.2 bags means buy 10.
Confusing cubic feet with cubic yards (off by 27×) when ordering bulk — a classic, expensive error.
Entering diameter where radius is expected on round beds — quadruples or quarters the result. Enter the diameter across the top; the tool halves it.
Eyeballing "times three" for several beds instead of letting the tool multiply precisely with the buffer applied.
Frequently asked questions
How much soil do I need for a 4x8 raised bed?
A 4 ft × 8 ft bed filled 10 inches deep holds 26.7 cu ft before settling. With a 15% buffer order ~30.7 cu ft (≈1.14 cu yd), about 21 bags at 1.5 cu ft. Filling only 6 inches drops it to ~18.4 cu ft (≈13 bags). Fill depth, not wall height, is the biggest driver.
How many bags of soil are in a cubic yard?
A cubic yard is 27 cu ft: about 27 bags @ 1.0 cu ft, 18 @ 1.5, 14 @ 2.0, or 9 @ 3.0 (rounded up). Around 9+ bags (≈14 cu ft / half a yard), bulk delivery is usually cheaper.
What's the best soil mix ratio for a raised bed?
Common starting recipes are 60/30/10, 50/40/10, and 40/40/20 (topsoil / compost / aeration or sand). "Aeration" means perlite, vermiculite, pumice, or coarse sand. The right ratio varies by crop and drainage — just avoid 100% compost or 100% topsoil in a deep bed.
How much settling buffer should I add?
Fresh mixes settle 10–20% the first season. Lightweight/soilless ~15–20%, blended garden mixes ~10–15%, pre-compressed bagged ~5–10%. The default 15% suits a typical blended mix.
Should I buy bagged or bulk?
Bagged is convenient for small fills; bulk (sold by the cubic yard, ~$40–80/cu yd in 2025–2026) is usually cheaper past ~14 cu ft (≈9+ bags). Enter both prices and the tool shows the exact dollar difference.
Do I measure the inside or outside of the bed?
Always the INTERIOR soil cavity, not the outside of the frame. For round beds and pots, enter the diameter across the top — the tool halves it to the radius for you.
Is it really free?
Yes — 100% free, and everything runs in your browser. It's a planning estimate: buy slightly over rather than under.