Raised Garden Bed Soil Calculator
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Find out how much soil your raised bed needs — cubic feet, cubic yards, bags, and a bagged-vs-bulk cost estimate.
Quick answer: Soil volume = length (ft) × width (ft) × depth (in ÷ 12). A common 4×8 ft bed filled 10 inches deep needs about 26.7 cubic feet — roughly 1 cubic yard, or about 18 bags of 1.5 cu ft bagged soil. "How to build a raised garden bed" gets 33,534+ impressions in our keyword research.
Soil Needed
📐 Formula
Volume (cu ft) = Length(ft) × Width(ft) × [Depth(in) ÷ 12]. Cubic yards = cubic feet ÷ 27. Bags needed = cubic feet ÷ 1.5, rounded up.
How to Use the Raised Garden Bed Soil Calculator
Enter your bed dimensions
Input the length and width of your raised bed in feet. If your bed isn't rectangular, measure the longest length and widest width for a close estimate, or split an irregular bed into rectangular sections and add the results.
Choose a fill depth
Set the fill depth in inches based on what you plan to grow. Shallow-rooted crops need less depth than root vegetables or tomatoes, so this single input has the biggest effect on total soil volume.
Review volume, bags, and cost
The calculator instantly shows cubic feet, cubic yards, how many standard 1.5 cubic foot bags you'd need, and an estimated cost range for both bagged and bulk soil purchases.
Adjust for your mix ratio
Use the result alongside the 60% topsoil / 30% compost / 10% aeration guideline below to work out roughly how much of each component to buy, and budget extra for settling.
Why Fill Depth Matters More Than Bed Size
Of the three numbers that go into this calculator, depth has the biggest impact on how much soil you'll actually buy, because it applies to the entire footprint of the bed at once — doubling the depth doubles the soil volume, while doubling the length only doubles it if the width stays the same. That makes the depth decision worth thinking through before you fill anything.
Shallow-rooted crops such as lettuce, spinach, most leafy greens, herbs, and radishes are comfortable in as little as 6–8 inches of loose soil. Their root systems stay close to the surface, so a shallow bed saves both soil and money without hurting yield. Root vegetables like carrots and beets, along with tomatoes, peppers, squash, and other heavier feeders, generally want 12–18 inches or more so their roots have room to develop fully and access enough nutrients and moisture through the season. A mixed vegetable bed growing a bit of everything is usually built somewhere in the 10–12 inch range as a practical compromise — deep enough for most crops, without paying for soil depth that only a handful of plants will use.
Worked Example: A 4×8 ft Bed at 10 Inches Deep
This is one of the most common raised bed sizes in the US, so it's worth walking through by hand. A bed measuring 4 feet by 8 feet, filled to a depth of 10 inches:
Step 1 — convert depth to feet: 10 in ÷ 12 = 0.833 ft.
Step 2 — multiply the three dimensions: 4 ft × 8 ft × 0.833 ft = 26.7 cubic feet.
Step 3 — convert to cubic yards (bulk soil is usually sold this way): 26.7 ÷ 27 = 0.99 cubic yards, essentially 1 full cubic yard.
Step 4 — convert to bags: 26.7 ÷ 1.5 = 17.8, rounded up to 18 bags of standard 1.5 cubic foot bagged soil.
At roughly $8–$10 per bag, 18 bags runs about $144–$180. At roughly $40–$55 per cubic yard delivered in bulk, the same volume (0.99 cubic yards) runs about $40–$54 before any delivery fee — a substantial saving once a bed approaches a full cubic yard, even after a modest delivery charge is added.
The 60/30/10 Soil Mix Ratio
A widely used rule of thumb among raised-bed gardeners is a mix of roughly 60% topsoil, 30% compost, and 10% aeration material such as perlite or vermiculite. This isn't a government or regulatory standard — it's just common horticultural practice that shows up again and again in gardening guides and extension publications, and it's a reasonable starting point rather than a fixed rule. The topsoil provides bulk and mineral content, the compost adds organic matter and nutrients that feed plants through the season, and the aeration material keeps the mix from compacting so roots and water can move through it freely.
For the worked example above, a 60/30/10 split of 26.7 cubic feet works out to roughly 16 cubic feet of topsoil, 8 cubic feet of compost, and 2.7 cubic feet of perlite or vermiculite. Gardeners often shift the ratio slightly — a bit more compost for heavy feeders like tomatoes, a bit more aeration material in a bed that tends to stay soggy. Treat 60/30/10 as a sensible default to adjust from, not a number to hit exactly.
Bagged vs. Bulk: Which Is Cheaper?
For a small bed needing only a handful of bags, bagged soil at around $8–$10 per 1.5 cubic foot bag is usually the more convenient choice — no delivery minimum, no leftover pile to deal with, and you can buy exactly what you need from a garden center or hardware store. Once a project approaches a full cubic yard or more, though, bulk delivery at roughly $40–$55 per cubic yard is almost always the cheaper option per cubic foot, even after a delivery fee is factored in. A single large bed, several beds built at once, or a bed with a deep fill depth are all situations where it's worth calling a local landscaping supplier for a bulk price before defaulting to bags.
Budget for Settling
Freshly filled soil doesn't stay at the level you poured it to. Compost continues breaking down, air pockets close up as the bed gets watered and walked around, and organic material compresses under its own weight — all of which cause the soil level to drop noticeably during the first season, sometimes by several inches in a deep bed. Most experienced gardeners budget about 10% extra soil volume up front to cover this, or simply plan to top the bed off with a bag or two of compost the following spring once things have settled. The calculator above includes this buffer as a separate line so you can see both the exact volume and the with-buffer figure at a glance.
Before and After You Fill the Bed
Once your bed is framed and filled, our garden pest identification guide is worth bookmarking before anything actually goes wrong — it's much easier to recognize early damage on a new bed than to diagnose it after a crop is already struggling. And if the same dimensions you just measured also need to cover a coat of paint elsewhere in the project — a shed, a trellis, a fence — the paint coverage calculator turns those same length/width numbers into gallons needed.
Frequently Asked Questions
Multiply length (ft) × width (ft) × depth (in ÷ 12) to get cubic feet, then divide by 27 for cubic yards. A common 4×8 ft bed filled 10 inches deep needs about 26.7 cubic feet, which is roughly 1 cubic yard, or about 18 bags of 1.5 cubic foot bagged soil. Add about 10% extra to cover settling in the first year.
A widely used gardening rule of thumb is roughly 60% topsoil, 30% compost, and 10% aeration material such as perlite or vermiculite. This isn't a government standard, just a common horticultural starting ratio — gardeners adjust it based on what they're growing and what compost is locally available. Heavy feeders like tomatoes often benefit from a higher compost share.
For small beds (a few bags' worth), bagged soil at roughly $8–$10 per 1.5 cubic foot bag is usually more convenient and avoids delivery minimums. For larger beds or multiple beds needing a cubic yard or more, bulk delivery at roughly $40–$55 per cubic yard is almost always cheaper per cubic foot, even after accounting for a delivery fee.
It depends on what you're growing. Shallow-rooted crops like lettuce, herbs, and most greens do fine in 6–8 inches of soil. Root vegetables, tomatoes, peppers, and other deep-rooted plants generally want 12–18 inches or more. A 10–12 inch depth is a common middle-ground choice for a mixed vegetable bed.
Yes. Fresh soil and compost settle and compress as organic matter breaks down and air pockets close up, typically dropping several inches in the first season. Most gardeners budget about 10% extra soil volume up front, or plan to top off the bed with a bag or two of compost the following spring.
Sources & Methodology
Soil volume figures are basic geometry (length × width × depth). Mix ratios and depth guidance reflect general horticultural practice as commonly published by the US Cooperative Extension Service — the state land-grant university extension offices that publish regional gardening guidance across the country — rather than a single fixed standard: