Jake Morrison, Licensed General Contractor · Last reviewed June 25, 2026

Raised Garden Bed Soil Calculator

Find out exactly how much soil it takes to fill your raised beds — in cubic feet, cubic yards, and bags — plus a mix recipe that tells you how many bags of compost, topsoil, and aeration to buy. Any shape, any number of beds, no signup.

Raised garden bed soil calculator: enter bed dimensions and soil mix

60% topsoil, 30% compost, 10% aeration. The all-purpose default for a new vegetable or flower bed.

Bed 1

ft
ft
in

Standard rectangular bed. Fill depth is how deep you're filling — measure at the corners, not the center.

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Enter your bed dimensions above to see how much soil you need — cubic feet, bags, cubic yards, and a mix recipe.

Estimates only. Soil settles 10–20% after the first few waterings, so round up and keep a spare bag for topping off. Confirm the bag volume on the label — a "soil" bag can be anywhere from 0.75 to 2.0 cu ft, which changes the bag count a lot. Measure fill depth at the corners, not the center, and don't count on filling all the way to the rim.

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How to use this calculator

  1. Pick your soil mix first. The mix you choose sets the recipe breakdown — how the total volume splits into compost, topsoil, peat/coir, vermiculite, or potting mix. The default standard mix (60% topsoil, 30% compost, 10% aeration) is a safe all-purpose choice for a first vegetable or flower bed. Mel's Mix (equal thirds compost, peat/coir, vermiculite) is the classic Square Foot Gardening recipe.
  2. Measure each bed. Pick the shape — rectangle, round, or oval — then enter the inside dimensions in feet and the fill depth in inches. Fill depth is how deep you actually intend to fill, which is often an inch or two below the rim, not the full height of the frame. You can add up to five beds and the tool sums them into one order.
  3. Choose how you're buying. Toggle between Bags (set the bag size — most bagged soil and compost is 1.5 or 2.0 cubic feet) and Bulk (cubic yards, for delivery). Small projects are almost always cheaper and easier in bags; once you pass roughly 12–15 bags, bulk delivery usually wins on price.
  4. Add a price (optional). Enter price per bag, or price per cubic yard in bulk mode, for a material-cost estimate. Bagged garden soil runs roughly $5–$12 per 1.5 cu ft bag; bulk garden-soil blends run $30–$60 per cubic yard delivered.
  5. Toggle settling if you want a buffer. Fresh soil and compost settle 10–20% after the first few waterings. Flip on "Add 10% for settling" and the tool pads the volume so your beds don't end up two inches low a week later.
  6. Read the result and grab the shopping list. You'll see total cubic feet, cubic yards, bag count, and a per-component breakdown — how many bags of each ingredient to put in the cart. Print or copy the branded PDF and take it to the garden center.

Why this raised bed soil calculator is different

Most "raised bed soil calculators" online give you a single cubic-feet number for one rectangular bed and stop there. After pulling the top results to compare, here's what's typical versus what this one adds:

  • It breaks the fill into a real mix recipe. No other calculator I found tells you how many bags of compost versus topsoil versus aeration to buy. That's the part people actually get wrong at the store — they buy 20 bags of "garden soil" and no compost. Pick a mix and this tool splits the order for you.
  • It sums multiple beds. Real gardens aren't one bed. Add a 4×8, a round herb planter, and an oval metal bed, and the calculator totals them into a single order so you make one trip.
  • It handles round and oval beds. Stock-tank planters are round; the popular metal raised beds (Vego-style) are oval. Rectangle-only calculators force you to fake those with a bounding box, which over-orders. This one uses the right geometry for each.
  • Bags vs. bulk, side by side. The single most useful decision for a soil order is "bags or bulk?" — and the answer flips based on volume. This tool shows you both the bag count and the cubic-yard figure so you can price it out either way.
  • It accounts for settling honestly. Soil drops after watering. The settling toggle is opt-in and clearly labeled at +10% — not a hidden multiplier baked into the headline number.
  • It's embeddable. If you run a gardening blog, a community-garden site, or moderate a subreddit, the iframe at the bottom lets you host the same calculator with attribution, free.

How it works (the math behind the numbers)

The core calculation is straight geometry, with depth converted from inches to feet:

rectangle   cu ft = length × width × (depth_in / 12)
round       cu ft = π × (diameter / 2)² × (depth_in / 12)
oval        cu ft = (π / 4) × length × width × (depth_in / 12)
cubic yards       = total cu ft / 27
bags              = ceil(total cu ft / bag size)

Every bed's volume is summed, the optional settling factor (×1.10) is applied to the total, and then the result is divided into bags (rounded up — you can't buy a partial bag) or expressed in cubic yards for bulk. The mix recipe takes that total and multiplies by each component's percentage: the Oregon State University Extension recommends a topsoil-plus-compost base for raised beds, and the Square Foot Gardening Foundation's Mel's Mix is equal thirds compost, peat moss (or coconut coir), and coarse vermiculite by volume. One cubic yard equals 27 cubic feet — that conversion is where a lot of hand calculations go wrong, because a yard of soil is a surprisingly large pile.

Three real-world examples

One 4×8 bed, 12 inches deep — the classic starter

A single 4×8 raised bed filled 12 inches deep is 32 cubic feet — about 1.2 cubic yards, or 22 bags at the common 1.5 cu ft size. In the standard mix that's roughly 13 bags of topsoil, 7 of compost, and 3 of an aeration amendment. That's a lot of bags to haul; at 32 cubic feet you're right at the edge where a bulk half-yard-rounded delivery starts to make sense if your supplier will drop that small a load.

Round stock-tank planter, 4 ft across, 10 inches deep

A galvanized stock-tank planter 4 feet in diameter, filled 10 inches deep, comes out to about 10.5 cubic feet — a tidy 6 bags at 2.0 cu ft each. Stock tanks drain poorly, so this is a case where you'd lean toward a lighter, faster-draining mix like Mel's Mix and make sure you've drilled drainage holes first. A cordless drill with a step bit is the right tool for that.

A three-bed garden — rectangle + round + oval

A real backyard setup: a 4×8 rectangle (32 cu ft), a 3-ft round herb planter 8 inches deep (≈4.7 cu ft), and a 6×3 oval metal bed 11 inches deep (≈13 cu ft). The calculator sums all three to about 50 cubic feet, or 1.85 cubic yards. At that volume you're firmly in "get it delivered in bulk" territory — 50 cubic feet is about 34 bags, which is most of a pickup bed and a sore back. While you're prepping, the right garden hose matters more than people think: you'll be watering in every bed deeply the day you fill them.

What affects how much soil you actually need

The calculator gives you a strong starting point, but a real fill has variables it can't see:

  • Settling. This is the big one. Fresh, fluffy soil and compost compact 10–20% after the first deep watering and the first rain. Always round up, and budget a spare bag or two for topping off two weeks later. The settling toggle bakes in a conservative 10%.
  • Fill depth vs. frame height. You rarely fill to the very top — leave an inch or two of freeboard so water and mulch don't wash over the edge. Enter your true intended fill depth, not the frame height.
  • Hügelkultur and fillers. If you're layering logs, branches, leaves, or cardboard in the bottom third (a common cost-saving technique for deep beds), you'll need substantially less purchased soil — sometimes 30–40% less. Reduce your fill depth in the calculator to just the soil layer.
  • Existing soil. Topping off an established bed that's settled? Switch to the "Top-off (all compost)" mix and enter only the depth you're adding, not the full bed depth.
  • Bag volume varies wildly. "Garden soil," "raised bed soil," "potting mix," and "compost" bags range from 0.75 to 2.0 cubic feet. The store sets the headline price per bag, but the cost per cubic foot is what matters — always check the label volume and set the right bag size here.
  • Moisture weight. A cubic foot of damp soil/compost weighs 40–50 lbs; a cubic yard is well over 1,000 lbs. If you're hauling bags, that's real weight on your vehicle and your back — another reason bulk delivery wins on larger jobs.

Note this is the calculator for filling a bed with soil. If you're still building the frame and need to know the lumber, screws, and corner hardware, that's a different calculation — browse Jake's full tool library for the materials estimators.

Frequently asked questions

How much soil do I need for a 4×8 raised bed?

For a 4×8 bed filled 12 inches deep, you need 32 cubic feet of soil — about 1.2 cubic yards, or roughly 22 bags at the common 1.5 cu ft size (16 bags at 2.0 cu ft). At 6 inches deep it's half that: 16 cubic feet. The fill depth drives everything, so measure how deep you actually plan to fill, not the height of the frame.

How many bags of soil are in a cubic yard?

One cubic yard is 27 cubic feet. So it takes 18 bags of 1.5 cu ft soil, 13–14 bags of 2.0 cu ft, or 36 bags of 0.75 cu ft to equal a cubic yard. This is exactly why bulk delivery gets cheaper than bags on bigger projects — once you're buying more than a dozen bags, you're paying a steep premium for the packaging and the trips.

What's the best soil mix for a raised garden bed?

For most vegetable and flower beds, a base of roughly 50–60% topsoil or garden soil, 30% compost, and 10–20% aeration (perlite or a quality potting mix) is hard to beat — it holds moisture and nutrients without compacting. Square Foot Gardeners swear by Mel's Mix (equal thirds compost, peat/coir, and coarse vermiculite), which is lighter and faster-draining but more expensive. Either way, compost is the ingredient people under-buy — don't skip it.

Should I buy soil in bags or in bulk?

Rule of thumb: under ~12–15 bags, buy bags; above that, get bulk delivered. Bags are convenient, clean, and let you buy exact mixes, but you pay a premium per cubic foot. Bulk soil is dramatically cheaper by volume but has a delivery minimum (usually 1 yard) and lands in a pile in your driveway that you have to move by wheelbarrow. This calculator shows both the bag count and the cubic-yard figure so you can compare.

Do I need to account for soil settling?

Yes. Fresh soil and compost are fluffy and full of air; after the first few deep waterings they compact 10–20%. A bed you filled to the brim will sit noticeably low within two weeks. Round your order up, keep a spare bag for topping off, or flip on the "+10% for settling" toggle in the calculator to build the buffer in automatically.

Beyond the soil itself, here's what makes a raised-bed fill day go smoothly:

  • Best Garden Hoses — every freshly filled bed needs a deep soak the same day to settle the soil and remove air pockets. A kink-free hose that reaches every bed saves a lot of cursing.
  • Best Cordless Drills — assembling raised-bed kits, drilling drainage holes in stock tanks, and driving corner hardware — the universal garden-build tool.
  • Best String Trimmers — keep the edges around and between raised beds clean where the mower can't reach.
  • Best Cordless Leaf Blowers — clearing spilled soil and mulch off paths and patios after a big fill takes minutes instead of a broom marathon.
  • Essential Tools for New Homeowners — the 12-tool starter kit before any DIY yard or garden project.

Sources & methodology

This calculator is reviewed annually for source currency. About Jake · Last reviewed June 25, 2026.

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Free for gardening blogs, community-garden and master-gardener sites, /r/gardening and /r/raisedbeds mods, garden-center and soil-supplier pages, and homestead renovation logs. Required attribution is included in the snippet. No fee, no account, no analytics attached to the embed. 

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