Raised bed soil calculator
Enter the inside size and height of your beds to get how much soil and how many bags to buy. We leave room below the rim and add 10% for settling.
Enter your measurements
More options: Settling · Mix · Bag price …
- Soil depth (filled)
- 11 in
- Soil to buy
- 32.3 cu ft (1.2 cu yd)
- Or order bulk garden blend
- 1.5 cubic yards
Soil depth: 12 in bed − 1 in below the rim = 11 in
8 ft × 4 ft × 11 in ÷ 12 = 29.3 cu ft (bed volume)
29.3 cu ft + 10% for settling = 32.3 cu ft
32.3 cu ft ÷ 1.5 cu ft per bag = 22 bags
Quick answers for common sizes
| Example | Answer |
|---|---|
| How much soil for a 4×8 raised bed | 32.3 cu ft |
| How much soil for a 4×8 raised bed 18 inches deep | 49.9 cu ft |
| How much soil for a 4×4 raised bed | 16.1 cu ft |
| How much soil for a 3×6 raised bed | 18.2 cu ft |
| How much soil for a 2×8 raised bed | 16.1 cu ft |
| How much soil for a 1.2 × 2.4 m raised bed | 871 L |
Soil for a bed of this size, by bed height
| Bed height (inside) | Soil to buy | Bags to buy |
|---|---|---|
| 6 in | 14.7 cu ft | 10 bags |
| 8 in | 20.5 cu ft | 14 bags |
| 10 in | 26.4 cu ft | 18 bags |
| 12 in | 32.3 cu ft | 22 bags |
| 18 in | 49.9 cu ft | 34 bags |
| 24 in | 67.5 cu ft | 45 bags |
Enter the bed’s real inside height and the calculator takes off the room you leave below the rim (1 in unless you change it). A 4 × 8 ft bed 12 in tall, filled 11 in deep, holds 29.3 cubic feet; the 10% on top is there because fresh, fluffy mix sinks noticeably after the first few waterings.
How the raised bed soil calculation works
A raised bed is a box, so the volume is length × width × soil depth, and the soil depth is the bed height minus the room you leave below the rim. With length and width in feet and depth in inches, divide the inches by 12. Multiply by the number of beds, then add an allowance for settling — bagged and freshly mixed soil is full of air and drops several inches in the first weeks.
soil depth = bed height − room below the rim cubic feet = length (ft) × width (ft) × soil depth (in) ÷ 12 × beds soil to buy = cubic feet × (1 + settling allowance) cubic yards = cubic feet ÷ 27
| Bed | 12 in of soil | 18 in of soil |
|---|---|---|
| 2 × 4 ft | 8 cu ft | 12 cu ft |
| 3 × 6 ft | 18 cu ft | 27 cu ft (1 yd³) |
| 4 × 4 ft | 16 cu ft | 24 cu ft |
| 4 × 8 ft | 32 cu ft | 48 cu ft |
| 4 × 12 ft | 48 cu ft | 72 cu ft |
Worked examples by bed size
Each of these pages covers what is specific to that size: the lumber it takes, where the bag count lands, and the usual mistake.
- How much soil for a 4×8 raised bed: the standard bed, and why a "12 inch" wooden frame is often only 11 in tall.
- How much soil for a 4×8 raised bed 18 inches deep: tall beds, bracing the long sides, and filling the bottom cheaply.
- How much soil for a 4×4 raised bed: the square-foot-garden box, including a 6 in Mel’s Mix fill.
- How much soil for a 3×6 raised bed: one-sided beds along a fence, and metal kits.
- How much soil for a 2×8 raised bed: narrow beds that dry out fast.
- How much soil for a 1.2 × 2.4 m raised bed: the metric 4 × 8, built from sleepers or boards.
Choosing a soil mix
Garden soil straight from the yard tends to compact in a box. Most raised-bed recipes blend a mineral soil with organic matter and something to keep it loose. University of Minnesota Extension suggests roughly half to two-thirds topsoil with the rest plant-based compost, and warns that too much compost holds excess water. Pick a recipe under More options and the calculator splits the volume for you. Common starting points:
- 60/30/10 — topsoil, compost, and an aerating material. Heavy enough to hold moisture, and the cheapest DIY option if you can get bulk topsoil.
- 50/50 topsoil and compost — simple and widely used for vegetables.
- Equal thirds (Mel’s Mix) — compost, peat moss or coir, and vermiculite. Light and very loose, but the bagged ingredients add up quickly for big beds.
- Bagged raised-bed mix — the least work. Check the bag size; they are usually 1–2 cu ft.
Tips
- Fill to about 1–2 in below the top edge so water and mulch have somewhere to sit — the calculator already subtracts it.
- Water each layer as you fill; dry peat and coir repel water at first.
- Expect to top up with an inch or two of compost each year as the organic matter breaks down.
Read how to fill a raised bed cheaply for layering methods that reduce the amount of purchased soil.
What you’ll need
- Galvanized metal raised bed kitMid-range price
Long-lasting and quick to assemble. Check the height — many kits are 12–17 in tall, which changes how much soil you buy.
See options on Amazon (opens in a new tab) - Cedar raised bed kitMid-range price
Naturally rot-resistant wood, easy to extend or stack for depth. Expect the boards to weather gray.
See options on Amazon (opens in a new tab) - Wheelbarrow (6 cu ft class)Mid-range price
Most home wheelbarrows hold 4–6 cubic feet — so a cubic yard of mulch is five or six trips. Two wheels are steadier on soft ground.
See options on Amazon (opens in a new tab) - Soil test kitBudget price
A quick read on pH and nutrients. For detailed results, many state extension labs offer inexpensive mail-in tests.
See options on Amazon (opens in a new tab) - Square foot garden gridBudget price
A ready-made 1 ft grid that sits on top of the bed so you can keep plant counts per square straight.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How much soil do I need for a 4 × 8 raised bed?
Every inch of soil in a 4 × 8 ft bed is 2.67 cubic feet. A bed 12 in tall filled to 1 in below the rim (11 in of soil) holds 29.3 cubic feet, or about 32.3 cu ft with 10% for settling; filled right to the top it would be 32 cu ft before settling. The bag counts are on How much soil for a 4×8 raised bed.
How many bags of soil for a raised bed?
Divide the soil volume in cubic feet (with the settling allowance) by the bag size. A 4 × 4 ft bed 12 in tall, filled 11 in deep, is 14.7 cu ft, so 11 bags of 1.5 cu ft with 10% extra — see How much soil for a 4×4 raised bed.
How deep should a raised bed be?
University of Missouri Extension says most plants need at least a 6–12 in rooting zone, and deeper is better. Root crops and tomatoes appreciate 12 in or more, especially over loosened ground. Deeper beds use a lot more soil, which is why some gardeners fill the bottom with organic material.
Why does raised bed soil sink?
Fresh mixes contain a lot of air, and organic matter breaks down over time. A settling allowance of 10–20% at the start, plus an annual compost top-up, keeps the bed full.
Related guides
Sources
- University of Minnesota Extension: Raised bed gardens (opens in a new tab) — Soil blend of roughly 1/2–2/3 topsoil and 1/3–1/2 plant-based compost; too much compost holds excess water.
- University of Missouri Extension: Raised-Bed Gardening (G6985) (opens in a new tab) — Four feet is a convenient width; about 3 ft if reached from one side; most plants need a 6–12 in rooting zone.
- Oregon State University Extension: Raised bed gardening (FS 270) (opens in a new tab) — Beds longer than about 6 ft should be reinforced so the soil doesn’t push the sides out.