How to easily calculate dirt for uneven ground or slope?

Filling in uneven or sloped ground isn’t just a matter of dumping soil – it’s about knowing exactly how much material you need, factoring in settling, and making sure the base will stay stable over time. Whether you’re expanding a driveway, leveling a garden area, or preparing a pad for a shed, an accurate calculation saves both money and headaches.
 

Below is a simple method to figure out how much fill dirt to order – with adjustments for slope shape and compaction.

What is fill dirt?

Fill dirt is a dense, mineral-rich subsoil layer located beneath topsoil. Unlike topsoil, it contains little to no organic matter, so it won’t decompose or shrink much over time. Because of its stability, it’s the go-to choice for:

• Raising low spots

• Leveling or reshaping uneven terrain

• Building a strong base under driveways, patios, or building pads

• Backfilling behind retaining walls

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Step-by-step: calculating fill dirt for uneven terrain

Step 1: Measure the area
You’ll need three measurements:

• Length (L) – the horizontal distance from one end of the fill area to the other

• Width (W) – side-to-side distance across the area

• Height (H) – the deepest vertical point you’ll need to fill

If you’re filling to a flat surface from a slope, the cross-section is shaped like a wedge (a triangle in profile).

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Step 2: Apply the wedge volume formula

Cubic feet = 0.5 × Length × Width × Height
Cubic yards = (0.5 × L × W × H) ÷ 27

Example:
You’re leveling a section of land that is:

• 50 feet long

• 18 feet wide

• 3 feet high at the deepest point

Calculation:

(0.5 × 50 × 18 × 3) ÷ 27
= (1,350) ÷ 27
= 50 cubic yards (before compaction allowance)
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Step 3: Add a compaction factor

Fill dirt always settles as it’s spread and compacted, so ordering extra is essential.

Typical allowances:

• 10–15% for screened, well-graded fill dirt

• 20–25% for loose or heavy clay soils

Example with 15% compaction:
50 × 1.15 = 57.5 cubic yards needed

Ordering 58 cubic yards ensures you won’t run short once the dirt is compacted.