Backfill Cubic Yard Calculator: How Much Soil?

This calculator works out the volume of backfill material you need in cubic yards, based on the length, width, and depth of the area you are filling. Enter those three dimensions in feet (or inches for depth), and it returns the cubic yards required, plus the equivalent in cubic feet and cubic meters for easy comparison. The result is the exact amount of soil, gravel, or sand to order for a rectangular excavation or trench.

Formula

The standard formula for backfill volume is:

Volume (yd³) = [Length (ft) × Width (ft) × Depth (ft)] ÷ 27

Where:

• Length is the longest horizontal dimension of the hole or trench, in feet.
• Width is the horizontal dimension perpendicular to length, in feet.
• Depth is how deep the fill goes, converted to feet (divide inches by 12).
• 27 is the number of cubic feet in one cubic yard (3 ft × 3 ft × 3 ft).

The calculator uses this exact formula, converting depth from inches to feet automatically. If you measure in meters, multiply the final cubic meters by 1.30795 to get cubic yards.

Worked Example

Using the default values: length = 10 ft, width = 5 ft, depth = 12 in.

1. Convert depth to feet: 12 in ÷ 12 = 1 ft
2. Calculate cubic feet: 10 × 5 × 1 = 50 ft³
3. Convert to cubic yards: 50 ÷ 27 = 1.85 yd³

The calculator shows 1.85 cubic yards, 50.0 cubic feet, and 1.42 cubic meters. That is the volume of material needed to fill the space completely level with the surrounding ground.

When to Use This Calculator

Use this tool for any rectangular backfill job: filling a foundation trench, leveling a low spot in a yard, filling a swimming pool hole, or bedding a retaining wall. It works for any free-flowing fill material—soil, sand, gravel, or crushed stone—because the volume calculation is the same regardless of what you pour in.

For irregular shapes, divide the area into rectangles, calculate each one, and add the results. For sloping ground, measure depth at the deepest point and the shallowest point, average them, and use that average as the depth. This gives a close estimate for most residential projects.

How to Measure Your Site Correctly

Accurate measurements matter more than the math. Follow these steps:

• Measure length and width at the top of the excavation, not the bottom, unless the walls are perfectly vertical. Most holes slope outward slightly.
• For a trench with sloped walls, measure the average width—halfway between top and bottom width.
• Depth should be the vertical distance from the ground surface to the bottom of the hole, not the length of a sloped wall.
• Use the same unit for all measurements. If you mix feet and inches, convert first (12 in = 1 ft).
• Add 10–15% for compaction. Most soils settle 10–20% after being dumped and tamped, so you will need more material than the raw volume.

For example, a 10×5 ft hole at 12 in deep needs 1.85 yd³ by calculation. With 10% compaction loss, order 2.0 yd³. With 20% loss, order 2.2 yd³. Suppliers usually sell in whole or half-yard increments, so round up to the nearest half yard.

Common Mistakes and How to Avoid Them

The most frequent error is mixing units. Depth is often given in inches while length and width are in feet—forgetting to divide by 12 throws the result off by a factor of 12. Another common mistake is using the bottom width of a sloped trench instead of the average width, which undercounts by a significant amount on deep excavations.

Rounding too early is also a problem. If you round 1.85 yd³ to 2 yd³ before adding the compaction factor, you end up short after settlement. Always calculate the raw volume first, then add the waste factor, then round up to the nearest order increment.

Finally, remember that this calculator gives the volume of the hole, not the volume of material after compaction. Loose fill occupies more space than compacted fill. The difference is the compaction factor mentioned above—it is not optional for most soils.

Cost and Ordering Considerations

Backfill material is typically sold by the cubic yard, either loose or delivered. To estimate cost, multiply the cubic yards by the per-yard price from your local supplier. Delivery fees are usually flat, so ordering slightly more than needed is cheaper than making a second delivery trip.

Most suppliers require a minimum order, often 1–2 cubic yards. For small projects, buying bagged soil from a garden center may be more practical—each bag is usually 0.75–1.0 cubic feet, and you would need 27 bags per cubic yard. For anything over a half yard, bulk delivery is almost always cheaper per unit volume.

Safety and Practical Tips

Backfill work involves heavy materials and open holes. Follow these basic safety practices:

• Never enter a trench deeper than 4 feet without proper shoring or sloping. Cave-ins are a leading cause of excavation fatalities.
• Keep the backfill pile at least 2 feet from the edge of the excavation to reduce the risk of collapse.
• Wear gloves and a dust mask when handling dry soil or gravel, especially if it contains silica dust.
• Compact in layers—spread 6–8 inches of fill, tamp it, then add the next layer. Dumping all at once leaves air pockets that settle later.
• Water helps compaction for clay soils but makes sandy soils unstable. Follow local practice for your soil type.

Frequently Asked Questions

How many bags of soil do I need for 1 cubic yard?

Standard garden soil bags hold 0.75 cubic feet (some hold 1.0 or 2.0). At 0.75 ft³ per bag, you need 36 bags for one cubic yard (27 ÷ 0.75). At 1.0 ft³ per bag, you need 27 bags. Check the bag label—it always lists the cubic foot volume.

Does this calculator work for gravel or sand?

Yes, the volume calculation is identical for any granular material. However, gravel and sand have different compaction factors—gravel compacts about 10%, sand about 15%. The calculator gives the raw volume; you still add your own waste factor.

Why do I need more backfill than the hole volume?

Because loose material settles. When you dig soil out, it expands (becomes fluffier). When you put it back and tamp it, it compresses again but not to its original density. The difference is typically 10–20% by volume, depending on soil type and how well you compact.

How do I calculate backfill for a round hole or pipe?

For a round hole (like a post hole), use the formula for a cylinder: π × radius² × depth, then divide by 27 to get cubic yards. For a pipe trench, subtract the pipe volume from the trench volume—calculate the trench as a rectangle and the pipe as a cylinder, then subtract.

What if my area is not a perfect rectangle?

Break it into smaller rectangles, calculate each one, and add the totals. For a triangle, use 0.5 × base × height × depth. For a circle, use π × radius² × depth. The calculator here is for rectangles only, but the math is simple to adapt.

Related

• Calculating Yards of Dirt: Formula and Examples
• Calculating Square Feet From Inches: Formula and Examples
• Calculating Square Meters: Formula and Examples

in l | Length | ft | 10 | 0
in w | Width | ft | 5 | 0
in d | Depth | in | 12 | 0
out yards | Cubic yards | yd³ | (l * w * (d / 12)) / 27 | 2
out cubic_ft | Cubic feet | ft³ | l * w * (d / 12) | 1
out cubic_m | Cubic meters | m³ | (l * w * (d / 12)) * 0.0283168 | 2