Raised Bed Soil Calculator
Volume, bags, and the fill mix that actually grows things. Free, instant, and private — everything runs on your device.
Your soil estimate
- Total volume
- 32 cu ft
- Topsoil / garden soil (60%)
- 19.2 cu ft
- Compost (30%)
- 9.6 cu ft
- Aeration — perlite/vermiculite (10%)
- 3.2 cu ft
- Estimated cost (bagged)
- $176
A good raised-bed mix is roughly 60% topsoil, 30% compost, 10% aeration. Over about 1 cubic yard, bulk delivery beats bags on price — the cubic-yard figure is there so you can compare.
The two ways people get raised-bed soil wrong: they buy bags of pure 'garden soil' that compacts into a brick, and they buy about a third of what the bed actually holds. This calculator fixes both. It converts your bed's real dimensions into cubic feet and yards, counts the bags, and — just as important — gives you the fill ratio that makes a bed productive instead of pretty-but-dead.
That ratio is roughly 60% topsoil or garden soil, 30% compost for fertility, and 10% aeration (perlite, vermiculite, or coarse bark) so roots get air and drainage. Fill multiple beds at once and the volume adds up fast — which is where bulk delivery starts beating bags.
How it works
No black box — this is the exact math the calculator runs.
- Volume = length × width × (depth in inches ÷ 12) × number of beds, in cubic feet.
- Cubic yards = cubic feet ÷ 27 — how bulk soil is sold and delivered.
- Bags = cubic feet ÷ bag size (1.5 cu ft default), rounded up.
- Recommended mix: 60% topsoil/garden soil, 30% compost, 10% aeration.
- Cost = bags × your price per bag; compare against bulk once you pass about a cubic yard.
Last reviewed July 24, 2026 · Garden & Landscaping
Frequently asked questions
How much soil do I need for a 4x8 raised bed?
A 4×8 bed filled 12 inches deep holds 32 cubic feet — about 22 standard 1.5-cu-ft bags, or 1.2 cubic yards. Filling only the top 6 inches over a base still needs 16 cubic feet, so bed depth matters a lot.
What is the best soil mix for a raised bed?
About 60% topsoil or quality garden soil, 30% finished compost, and 10% aeration like perlite or coarse vermiculite. Pure bagged 'garden soil' or straight topsoil compacts and drowns roots; pure compost is too rich and shrinks as it breaks down.
Should I buy bagged soil or bulk?
Under about one cubic yard, bags are convenient and similar in price. Past a yard — which a single 4×8 bed nearly reaches — bulk delivery is usually cheaper per yard, if you have somewhere to dump the pile and a wheelbarrow to move it.
Do I need to fill a raised bed all the way with soil?
You can fill the bottom of a deep bed with coarse organic matter (the 'hugelkultur' method) — logs, branches, leaves — then top with your soil mix. It saves soil and adds long-term fertility, but the material settles, so plan to top up next season.