Garden Bed Volume Calculator: Cubic Yards & Feet

This calculator works out the volume of soil, compost, or mulch needed to fill a raised garden bed or planter. You enter the bed’s length and width in feet and the desired soil depth in inches, and it returns the volume in both cubic yards and cubic feet.

Formula

The volume of a rectangular garden bed is length × width × depth. Because you enter length and width in feet but depth in inches, the formula converts inches to feet first:

Volume (ft³) = L × W × (D ÷ 12)

Volume (yd³) = L × W × (D ÷ 12) ÷ 27

Where:

• L = length of the bed in feet (ft)
• W = width of the bed in feet (ft)
• D = depth of soil in inches (in)

The conversion factors are fixed: 12 inches per foot, and 27 cubic feet per cubic yard. The calculator applies both automatically, so you never have to convert units yourself.

Worked Example

Using the default values from the calculator — a bed 40 ft long, 25 ft wide, and 3 in deep — the calculation goes like this:

1. Convert depth to feet: 3 in ÷ 12 = 0.25 ft
2. Multiply length × width × depth: 40 × 25 × 0.25 = 250 ft³
3. Convert to cubic yards: 250 ÷ 27 = 9.26 yd³

The calculator shows 9.26 cubic yards and 250.0 cubic feet for those inputs. If you buy soil in bags, each bag typically holds 1 or 2 cubic feet, so 250 ft³ would mean 250 one-cubic-foot bags or 125 two-cubic-foot bags. For bulk delivery, order about 9.5 cubic yards to account for settling and spillage.

Why Depth Matters More Than You Think

Most gardeners underestimate how much soil a bed actually needs because they focus on length and width. A 4×8 ft bed at 6 inches deep needs 16 cubic feet of soil; at 12 inches deep, it needs 32 cubic feet — double. That difference changes whether you buy 8 bags or 16, or whether a single cubic-yard delivery covers one bed or two.

Root depth is the real deciding factor. Shallow-rooted crops like lettuce and radishes grow fine in 6 inches of soil. Tomatoes, peppers, and carrots want 12 inches or more. If you’re building a bed on top of grass or hard ground, add a few extra inches so roots can establish. If the bed sits on good native soil, you can subtract a few inches because plants can grow down into the ground below.

How to Measure a Garden Bed Correctly

Measure the inside dimensions of the bed, not the outside. The frame boards add width that doesn’t hold soil. Use a tape measure and record the length and width in feet, rounding to the nearest inch. For depth, measure from the top edge of the frame down to where the soil will actually sit — if you plan to leave 1 inch of space below the rim to prevent overflow, subtract that from the frame height.

For L-shaped or U-shaped beds, split the shape into rectangles, calculate each volume separately, then add them together. For triangular corners, use ½ × base × height × depth. Odd shapes are easier to handle by breaking them into smaller rectangles than by trying to measure the whole outline at once.

Common Mistakes When Calculating Bed Volume

• Mixing units: Entering depth in inches while length is in feet without converting. This overestimates volume by 12×.
• Using outside dimensions: Adding 2–4 inches of frame width to every side inflates the volume by 5–15%.
• Forgetting settling: Fresh soil, especially compost or bark, settles 10–20% after watering. Add that much extra to your order.
• Rounding too early: If you round 9.26 yd³ down to 9 yd³, you’re short by 7 cubic feet — about 4 bags.
• Assuming all bags are 1 ft³: Many retail bags hold 1.5 or 2 ft³. Check the label before calculating how many to buy.

Bulk Soil vs. Bags: What the Number Tells You

Cubic yards are the standard unit for bulk deliveries from landscape suppliers. A cubic yard is 27 cubic feet, roughly the size of a washing machine. Most small pickup trucks carry 1–2 cubic yards; larger dump trucks carry 10–15. If your volume exceeds about 2 cubic yards, delivery is usually more practical than hauling bags.

Bags are sold by cubic foot, so the calculator’s cubic-foot output is what you use to count bags. Divide the total cubic feet by the bag size (1, 1.5, or 2 ft³) and round up to the nearest whole bag. For a 4×8×1 ft bed (32 ft³), that’s 32 one-cubic-foot bags, 22 two-cubic-foot bags, or about 1.2 cubic yards bulk. Bulk is almost always cheaper per cubic foot, but you must be able to move and spread it the same day.

When the Calculator Doesn’t Apply

This formula assumes a rectangular bed with vertical sides and a flat bottom. It does not work for:

• Round or oval beds: Use Ï€ × radius² × depth instead.
• Tapered planters: If the top is wider than the bottom, use the average of the two widths.
• Raised beds on legs: These are usually smaller and measured in quarts or liters, not cubic yards.
• Wicking beds: The water reservoir at the bottom reduces the soil volume; subtract that layer’s height from the depth.

Also note that soil volume shrinks after the first watering. A bed filled to the brim will settle 1–2 inches within a week. Most gardeners fill slightly above the desired depth and expect to top up later.

Frequently Asked Questions

How many cubic feet are in a cubic yard?

There are 27 cubic feet in 1 cubic yard (3 ft × 3 ft × 3 ft). To convert, divide cubic feet by 27. The calculator does this automatically for the cubic-yard output.

How deep should a raised garden bed be?

For most vegetables, 12 inches is ideal. Six inches works for shallow-rooted greens and herbs. If the bed sits on concrete or compacted gravel, go at least 18 inches so roots have enough room to grow downward.

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

At 12 inches deep, a 4×8 ft bed needs 32 cubic feet (4×8×1). That’s 1.19 cubic yards or about 16 two-cubic-foot bags. At 6 inches deep, it needs 16 cubic feet — half that amount.

Should I fill the whole bed with soil?

No. Many gardeners put coarse wood chips, logs, or leaves in the bottom 6–12 inches to save soil and improve drainage. This is called hugelkultur. If you do that, measure only the soil layer’s depth, not the full frame height, when calculating volume.

How much does a cubic yard of soil weigh?

Dry topsoil weighs about 1,000–1,200 pounds per cubic yard; wet soil can weigh 1,500–2,000 pounds. Compost is lighter at 800–1,000 pounds. This matters for delivery trucks and for whether your deck or balcony can support the weight.

Can I use this calculator for mulch or compost?

Yes. The volume math is the same for any loose material. Just enter the depth you want to spread — 2–3 inches for mulch, 1–2 inches for compost — and use the cubic-foot output to count bags or the cubic-yard output for bulk orders.

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in l | Lawn length | ft | 40 | 0 | 100000
in w | Lawn width | ft | 25 | 0 | 100000
in d | Depth | in | 3 | 0 | 120
out yd | Volume | yd³ | l * w * d / 324 | 2
out ft3 | Volume | ft³ | l * w * d / 12 | 1