Multiple Beds · Blend Splits · Bag Counts · Cost
Raised Bed Soil Calculator — Beds, Blends & Bag Counts
Total cubic yards across any number of beds, split into per-component volumes for 60/30/10, 50/50, or Mel's mix — with board-thickness deduction, bag counts per ingredient, and the full bill.
Input Parameters
Bed size presets (external)
Fill height (soil depth)
Board thickness (deducted from volume)
Internal size: 3.75 × 7.75 ft — external minus two board thicknesses per side.
Soil Blend
The standard recommendation for vegetable beds: topsoil body, compost fertility, drainage insurance.
Component Pricesoptional
typ. $20–40/yd bulk
typ. $25–50/yd bulk
bagged vermiculite ≈ $120–190/yd eq.
Your Blend Estimate
Total soil to order
2.37
cu yd · 64 cu ft · incl. +10% settling
Volume
38.4 cf
Bags
26
Cost
$43
Volume
19.2 cf
Bags
13
Cost
$27
Volume
6.4 cf
Bags
5
Cost
$37
Per bed
29.1 cf
1.08 yd³ each
Base total
2.15 yd³
58 cf before settling
Total bags
44
1.5 cu ft bag
Approx weight
5,281 lb
deck-load planning figure
Bulk $/yd planning defaults — aeration & peat are usually bagged at retail; swap in your local quotes before ordering.
Filling raised beds is step two. If the project starts from lawn or bare ground, the dirt calculator on the Dirt Calculator homepage estimates the grade-up fill underneath, and the Calculators hub lists every companion tool — topsoil, mulch, gravel, and excavation.
Bed Geometry & Board Thickness: Volume You Actually Fill
Soil fills the inside of the frame, not the footprint of the plan. Boards consume real volume: 1.5-inch lumber steals 3 inches from a bed's length and 3 from its width (two boards per side), so a nominal 4×8 bed holds 3.75 × 7.75 feet of soil — 29.06 cubic feet at a 12-inch fill against the 32 cubic feet the external dimensions suggest. On a single bed that is a bag of soil; across a garden of eight beds it is two-thirds of a cubic yard, roughly $25 of blend that never needed buying. The calculator deducts twice the board thickness from each dimension before any volume math runs.
Fill height carries the same nominal-vs-actual trap. A "2×6" board measures 5.5 inches tall at the lumber yard, so two stacked courses give an 11-inch wall — fill to 10 inches and you keep a rim for mulch and watering. The table below lists internal volumes for the five most common bed footprints at three fill heights, all with 1.5-inch boards deducted; read the exact cell and the bag counts fall out directly.
| Bed (nominal) | Internal size | 6" fill | 12" fill | 16" fill |
|---|---|---|---|---|
| 2×4 ft | 1.75 × 3.75 ft | 3.3 cf · 0.12 yd³ | 6.6 cf · 0.24 yd³ | 8.8 cf · 0.32 yd³ |
| 3×6 ft | 2.75 × 5.75 ft | 7.9 cf · 0.29 yd³ | 15.8 cf · 0.59 yd³ | 21.1 cf · 0.78 yd³ |
| 4×4 ft | 3.75 × 3.75 ft | 7.0 cf · 0.26 yd³ | 14.1 cf · 0.52 yd³ | 18.8 cf · 0.69 yd³ |
| 4×8 ft | 3.75 × 7.75 ft | 14.5 cf · 0.54 yd³ | 29.1 cf · 1.08 yd³ | 38.8 cf · 1.44 yd³ |
| 4×12 ft | 3.75 × 11.75 ft | 22.0 cf · 0.82 yd³ | 44.1 cf · 1.63 yd³ | 58.8 cf · 2.18 yd³ |
Internal volumes with 1.5" lumber deducted; cubic feet ÷ 27 = cubic yards. Counts before settling allowance — add 10% for first-season settling or use the calculator slider.
Tip: measure the actual board
A calipers-or-tape check of your lumber takes 30 seconds. Cedar 1× boards often run 0.72"; rough-sawn 2" stock really is 2". The deduction only protects you if the thickness is real.
Warning: the 2×6 trap
Planning a 12-inch-deep bed out of two 2×6 courses? You have 11 inches of wall. Setting the fill height to 12" quietly over-orders by 9% — set 10–11" or add a 2×2 cap course.
Don't: gravel the bottom
Gravel under bed soil forms a perched water table that rots roots — the opposite of the drainage it promises. If drainage matters, skip the stones, raise the fill height, and let the aeration fraction of the blend do the work.
Boards eat volumePhoto: UnsplashWhy bed count matters more than bed size
Two 4×8 beds hold the same soil as one 8×8 — but four beds at 12 inches hold 1.61 cubic yards more than one 4×8, because soil scales with count × footprint × height. Multiply first, then order once.
Common Raised Bed Blends: 60/30/10, 50/50 & Mel's Mix
A raised bed is a container, and its soil is a recipe rather than a product. The three blends below cover nearly every home garden decision. The 60/30/10 blend is the default recommendation — topsoil for body, compost for fertility, and aeration material so the mix keeps breathing after compost decomposes. The 50/50 blend is the budget version that works in beds with naturally loose native soil. Mel's mix — one third each of blended compost, sphagnum peat moss, and coarse vermiculite — is the published Square Foot Gardening recipe (source: Square Foot Gardening Foundation, squarefootgardening.org); it contains no topsoil, holds water like a sponge, and costs three to four times as much per yard because peat and vermiculite only retail in bags.
| Blend | Component A | Component B | Component C |
|---|---|---|---|
| 60 / 30 / 10 | 17.4 cf · 0.65 yd³ · 12 bags | 8.7 cf · 0.32 yd³ · 6 bags | 2.9 cf · 0.11 yd³ · 2 bags |
| 50 / 50 | 14.5 cf · 0.54 yd³ · 10 bags | 14.5 cf · 0.54 yd³ · 10 bags | — · 0 bags |
| Mel's mix (1/3 each) | 9.7 cf · 0.36 yd³ · 7 bags | 9.7 cf · 0.36 yd³ · 7 bags | 9.7 cf · 0.36 yd³ · 7 bags |
Split for one 4×8 bed at 12" fill (29.06 cu ft internal); bags are 1.5 cu ft counts. Scale linearly with bed count — or set the blend above and let the calculator multiply.
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60/30/10 — the workhorse
Best for 12-inch vegetable beds that must hold moisture through summer. The topsoil share gives water-holding structure; compost feeds a full season; the aeration share keeps root-zone oxygen above 10% after the first year's settling.
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50/50 — the budget build
Two ingredients, one delivery if the yard sells both. Works where native soil is already sandy or loamy; skip it over clay, where compost-heavy mixes stay waterlogged in spring and crack in August.
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Mel's mix — the square-foot build
Weightless and uniform — 6 inches grows anything a square-foot grid plants. The cost is real: a 4×8 bed at 6 inches needs 14.5 cu ft of mix, about $150–230 in retail bags, versus $55–90 for a bulk 60/30/10 fill.
Depth follows rootsPhoto: UnsplashThe one-inch rule
Whatever the wall height, fill to 1 inch below the rim. That inch is where water goes during a slow soak instead of over the sides — a full-to-the-brim bed loses every irrigation to runoff.
Fill Height: Match the Bed to the Root, Not the Lumber
Depth is the most expensive variable in a raised bed and the least understood. Roots do not dig — they thread through loose soil and stop where oxygen or resistance stops them, which is why fill height, not wall height, decides what grows well. Six inches grows every leaf crop and most herbs; ten to twelve inches carries the fruiting vegetables; sixteen inches or more only earns its cost for long carrots, parsnips, and potatoes grown for storage. Below the fill, roots happily continue into soft native ground — a 12-inch bed of loose blend over decent subsoil outgrows a 20-inch bed of the same blend sitting on compacted gravel.
| Crop family | Working root depth | Fill height to aim for | Notes |
|---|---|---|---|
| Lettuce, spinach, herbs | 4–6" | 6" | Shallowest rooters; 6 inches of blend dries evenly |
| Onions, garlic, radish | 6–8" | 8" | Bulbs sit at the surface — depth buys weeds nothing |
| Beans, peas, beets, brassicas | 8–12" | 10" | The 10-inch default covers most of a kitchen garden |
| Tomatoes, peppers, eggplant | 12–18" | 12–16" | Deep blend holds moisture between summer waterings |
| Carrots, parsnips, potatoes | 12–18" | 16" | Long varieties need uniform, stone-free depth |
| Dwarf fruit & perennials | 18–24" | 18"+ | Perennials want the deepest, richest fill you'll pay for |
Deep beds without deep cost
Beds framed at 18–24 inches do not need 24 inches of $35-per-yard blend. The bottom third can be coarse wood chips, sticks, or half-rotted logs — roots spend their first season in the top 12 inches anyway, and the buried wood slowly becomes sponge-like humus (the Hugelkultur approach). Fill the calculator's height with the true planting depth and price the sub-fill separately: a 4×8 bed at 24 inches costs about $180 to fill entirely with blend, versus $120 with a chip bottom third. What never belongs at the bottom is gravel — it raises, not drains, the water line.
Per-bed fill quick answers (with 1.5" boards, before allowance)
- 4×4 at 6": 7.0 cf — five 1.5 cf bags
- 4×4 at 12": 14.1 cf — ten 1.5 cf bags
- 4×8 at 6": 14.5 cf — 0.54 yd³ bulk
- 4×8 at 12": 29.1 cf — 1.08 yd³ bulk
- 4×12 at 12": 44.1 cf — 1.63 yd³ bulk
Bags vs. Bulk: Where Raised Beds Break the Usual Rule
For plain topsoil the bag-vs-bulk breakeven sits near one cubic yard, and raised beds are where the bag side of that line is unusually wide — but the blend breaks the rule. A component-split order is hard to buy in bulk: suppliers sell topsoil and compost by the yard, but perlite, vermiculite, and peat only come bagged, and asking a landscape yard to pre-blend 60/30/10 means trusting their compost's weed seed and moisture sight-unseen. Many bed builders therefore run hybrid logistics: bulk topsoil and compost delivered, bags of aeration material added and mixed in the wheelbarrow per bed.
The cost comparison at the 4×8/12-inch scale: 1.08 cubic yards of pre-blended bulk mix at $32/yd delivered is about $80 including a shared-load freight split; the same volume in bags is 29 cubic feet — twenty bags of topsoil, ten of compost, two of aeration — running $110–140 at big-box pricing. Bulk wins on price at anything above two beds; bags win on control, timing (fill one bed per weekend), and access to fenced backyards where a dump truck cannot reach. The calculator's bag counts per component exist precisely for the hybrid approach — order the bulk yards for the two heavy components, then shop bags for the rest.
One 4×8 @ 12"
≈ $80 bulk · $110–140 bagged
Bulk only wins if freight is shared with other yard projects — minimum-load clauses make a solo one-yard delivery surprisingly expensive.
Four 4×8 @ 12"
≈ $180 bulk · $440–560 bagged
At four beds the gap is a factor of three — this is where a delivered pile of topsoil and compost plus bagged aeration becomes the obvious play.
Mel's mix, any scale
Bag-only, realistically
Peat bales and vermiculite bags are the only retail channel. A 4×8 at 6 inches of true Mel's mix runs $150–230 — price it before committing to the recipe.
What a Raised Bed Actually Costs to Fill
Filling costs scale with two decisions: the blend recipe and the fill height. The component prices in the calculator — topsoil $20–40/yd, compost $25–50/yd, aeration material $120–190/yd-equivalent, peat $110–145/yd-equivalent — produce a finished-blend range of roughly $30–45 per cubic yard for 60/30/10, $33–48 for 50/50, and $110–160 for Mel's mix. Height multiplies those unit costs linearly: doubling a 4×8 bed from 6 to 12 inches doubles the fill bill exactly, with no economies of scale inside a single bed. The economies live in the delivery instead — one truck carrying four beds' worth of topsoil and compost pays freight once.
Worked example — two 4×8 beds at 12 inches, 60/30/10 blend, 10% settling allowance. Internal volume per bed is 29.1 cubic feet, base total 58.1 cubic feet, order quantity 64 cubic feet, or 2.37 cubic yards. The split: 1.42 yards of topsoil at $30 ($43), 0.71 yards of compost at $38 ($27), and 0.24 yards of aeration at $155 ($36). Material total about $106 — plus freight on a small bulk order, or about 43 bags of 1.5 cu ft blend if bought bagged. The results panel reproduces this line by line for any bed count, so the number to hand the supplier is checkable rather than guessed.
| Scenario | Blend | Soil volume | Material cost | With delivery |
|---|---|---|---|---|
| One 4×8 @ 6" | 60/30/10 | 0.59 yd³ | ≈ $21 | ≈ $115 (min load) |
| One 4×8 @ 12" | 60/30/10 | 1.19 yd³ | ≈ $42 | ≈ $137 (min load) |
| Two 4×8 @ 12" | 60/30/10 | 2.37 yd³ | ≈ $106 | ≈ $200 |
| Four 4×8 @ 12" | 60/30/10 | 4.75 yd³ | ≈ $211 | ≈ $310 |
| One 4×8 @ 6" | Mel's mix | 0.59 yd³ | ≈ $75 (bags) | bags / pickup |
Scenario table at $30/yd topsoil, $38/yd compost, $155/yd aeration-equivalent, $95 regional delivery fee. All planning defaults — real quotes vary by region and season.
Buying the blend, not the marketing
- 1. "Raised bed soil" in bags is potting mix at $8–15/cu ft — 5–8× the bulk equivalent. Read the ingredient list before paying for the label.
- 2. Ask the compost supplier what went into the pile: food-waste and mushroom compost feed soil; mixed-waste compost can carry herbicide residue that kills tomatoes.
- 3. One delivery of each component beats "premium bed blend" deliveries on price and lets you verify each ingredient.
- 4. Budget a yearly top-up of 10–15% of bed volume in compost — settling does not stop after year one.
Raised Bed Soil Questions, Answered With Numbers
Bed volumes, blend splits, board deductions, and bag math — each answer reproducible in the calculator above.
How much dirt do I need for a 4×8 raised bed?
How many bags of soil do I need for a raised bed?
How much soil for a raised garden bed per square foot?
What is Mel's mix, and how much do the ingredients cost?
Is 60/30/10 the right soil ratio for raised beds?
How deep should a raised bed be for vegetables?
Do I subtract the board thickness from the bed volume?
Why is a 2×6 board not 6 inches tall?
How much does the soil in a raised bed weigh?
Should I fill the whole bed with soil or use fill at the bottom?
Does raised bed soil settle?
Can I use potting mix in raised beds?
Data & sources: volume math uses fixed unit conversions (1 yd³ = 27 cu ft) and the site engine's constants; topsoil and compost price bands mirror the site material table ($20–40/yd and $25–50/yd). Mel's mix follows the published Square Foot Gardening recipe (Square Foot Gardening Foundation, squarefootgardening.org — 1/3 compost, 1/3 peat, 1/3 coarse vermiculite). Nominal-vs-actual lumber sizes per standard dressed-dimension rules.
Planning estimates to verify locally: component price defaults (peat, vermiculite, perlite bag-derived equivalents), bag pricing, and blend densities used for the weight figure — all labeled typical ranges, not quotes.
Author: Dirt Calculator editorial team · Last updated: October 26, 2026. Planning aid only — crop outcomes depend on local soil and climate.
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