Cubic Feet Calculator for Soil: How Much Do You Need?

A cubic feet calculator for soil works out the volume of soil you need to fill a space, and you enter the length, width, and depth of the area in feet (or inches) to get the answer in cubic feet. This is the number you use when buying bagged soil or converting to cubic yards for bulk delivery. The calculator below does exactly that, and it also shows the result in cubic yards so you can compare bag counts with bulk pricing.

Formula

The formula for soil volume is straightforward: Volume (cubic feet) = Length (ft) × Width (ft) × Depth (ft). Because depth is usually measured in inches, you first convert it to feet by dividing by 12. The full formula becomes:

Cubic feet = L × W × (D / 12)

Where:

• L = length of the bed or container, in feet
• W = width, in feet
• D = depth of soil, in inches (converted to feet by dividing by 12)

If you measure everything in inches, the formula is cubic inches ÷ 1728 (since 1 cubic foot = 12 × 12 × 12 = 1728 cubic inches). For cubic yards, divide cubic feet by 27 (1 yard = 3 feet, so 3 × 3 × 3 = 27).

Worked Example

Using the default values from the calculator above: a raised bed that is 10 feet long, 4 feet wide, and you want a 6-inch depth of soil.

1. Convert depth to feet: 6 inches ÷ 12 = 0.5 ft
2. Multiply: 10 × 4 × 0.5 = 20 cubic feet
3. Convert to cubic yards: 20 ÷ 27 = 0.74 cubic yards
4. Bag count (1.5 cu ft bags): 20 ÷ 1.5 = 13.33, so you need 14 bags

The calculator returns 20.00 cubic feet, 0.74 cubic yards, and 14 bags. That matches the manual calculation.

Why Soil Volume Matters

Soil is heavy and expensive to move, so over-ordering wastes money and under-ordering leaves you short. Volume is the only fair way to compare bagged soil (sold in cubic feet) with bulk soil (sold in cubic yards). A common mistake is confusing cubic feet with square feet: a 10×4 bed is 40 square feet, but with 6 inches of soil it only needs 20 cubic feet. Another frequent error is mixing units—multiplying a length in feet by a width in inches without converting.

For raised beds, the depth you choose depends on what you grow. Shallow-rooted herbs need about 6 inches; tomatoes and shrubs prefer 12–18 inches. If your bed sits on grass or hard ground, you may need more soil than the bed’s own height because the soil settles. Fresh bagged soil often compacts by 10–20% after watering, so buying 10% extra is a common practice.

How to Measure Your Space

Measure the inside dimensions of the bed, not the outside. For rectangular beds, measure length and width at the top, and depth from the top edge to the bottom. For circular planters, measure the diameter and use the formula for a cylinder: π × (radius in ft)² × depth in ft. For triangular or irregular shapes, break the area into rectangles and triangles, calculate each volume, and add them together.

If you are filling a container with tapering sides (like a pot that is wider at the top), measure the average of the top and bottom diameters for a close estimate. For a truly accurate result, you can line the container with a plastic bag and pour in measured water, but that is messy and rarely needed.

Bag Size and Coverage

Bagged soil is sold in various sizes, commonly 0.75, 1.0, 1.5, and 2.0 cubic feet. The calculator uses 1.5 cu ft as a default, but you can adjust the bag size in the formula if yours differs. To find how many bags you need, divide the total cubic feet by the bag volume and round up. For example, 20 cubic feet with 2 cu ft bags gives 10 bags exactly. With 0.75 cu ft bags, you would need 27 bags (20 ÷ 0.75 = 26.67).

Bulk soil is delivered by the cubic yard (27 cubic feet). A typical small dump truck holds 1–2 yards, and a full-size pickup can carry about 1 yard safely. Bulk is usually cheaper per cubic foot than bags, but you must order the right amount and have a place to dump it. For small projects under 1 cubic yard, bags are often more practical.

Common Mistakes and How to Avoid Them

• Mixing units: Always convert inches to feet before multiplying. 6 inches is 0.5 ft, not 6 ft.
• Forgetting to divide by 27 for yards: A cubic yard is 27 cubic feet, not 3. Many people mistakenly divide by 3.
• Using outside dimensions: The soil only fills the inside of the bed, so measure the interior.
• Ignoring settling: Soil compacts after watering. Add 10–15% extra if you want the final level to match the top.
• Rounding too early: Keep full precision until the final step, then round up for bag counts.

When the Simple Formula Isn’t Enough

The length × width × depth formula assumes a rectangular prism with straight sides and a flat bottom. Real-world beds may have sloped sides, rounded corners, or uneven ground. For a sloped bed, measure depth at several points and use the average. For a bed with a V-shaped bottom, treat it as half a rectangular prism. If you are filling a large area with a depth that varies, divide the area into sections, calculate each, and sum them.

Also note that the formula gives the volume of the space, not the weight of the soil. A cubic foot of dry topsoil weighs roughly 75–100 pounds, but wet soil can weigh 110 pounds or more. If you are moving bags or planning a delivery, consider weight limits for your vehicle or the structural strength of a balcony or rooftop garden.

Frequently Asked Questions

How many cubic feet are in a 5-gallon bucket? A 5-gallon bucket holds about 0.67 cubic feet (since 1 gallon = 0.134 cubic feet). For soil, that is roughly 40–50 pounds of dry mix. Many gardeners use 5-gallon buckets as a measure for small containers.

What is the difference between topsoil, garden soil, and potting mix? Topsoil is the natural upper layer of soil, often used for filling large areas. Garden soil is topsoil enriched with compost, meant for in-ground beds. Potting mix is a soilless blend (peat, perlite, compost) designed for containers because it drains well and doesn’t compact. The volume calculation is the same for all, but the weight and cost differ.

How much soil do I need for a 4×4 raised bed? For a 4×4 bed with 6 inches of soil, you need 8 cubic feet (4×4×0.5). That is about 6 bags of 1.5 cu ft, or 0.3 cubic yards. For 12 inches deep, double it to 16 cubic feet.

Should I buy bags or bulk soil? Bags are easier for small projects, allow you to mix types, and are available at garden centers. Bulk is cheaper per cubic foot for large areas (typically over 1 cubic yard) but requires delivery or a truck, and you must use it quickly to avoid it drying out or washing away.

How much does a cubic yard of soil weigh? A cubic yard of dry topsoil weighs about 2,000–2,700 pounds (1–1.35 tons). Wet soil can weigh up to 3,000 pounds. This matters for delivery trucks and for garden beds on decks or balconies—check weight limits.

Does soil settle after planting? Yes, most soil mixes settle 10–20% after the first few waterings. That is why it is wise to add a little extra or top up later. If you want the final soil level to be exactly at the bed rim, buy about 10% more than the calculated volume.

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in l | Length | ft | 10 | 0
in w | Width | ft | 4 | 0
in d | Depth | in | 6 | 0
out cuft | Cubic feet of soil | cu ft | l * w * (d / 12) | 2
out cuyd | Cubic yards | cu yd | (l * w * (d / 12)) / 27 | 2
out bags | 1.5 cu ft bags needed | bags | ceil((l * w * (d / 12)) / 1.5) | 0