How To Calculate Fill Dirt On A Slope
Published on: June 16, 2025
How to Calculate Fill Dirt for a Slope (Accurately and Easily)
Filling in a slope isn’t just about dumping dirt—it’s about getting the right amount, accounting for settling, and making sure your base is stable. Whether you’re leveling a backyard, grading a construction site, or prepping for a foundation, knowing how much fill dirt to order will save time, money, and stress.
Here’s a clear, step-by-step method to calculate how much fill dirt you’ll need—plus how to adjust for slope shape and compaction.
What Is Fill Dirt, Exactly?
Fill dirt is the dense, mineral-rich layer of subsoil found beneath topsoil. Unlike topsoil, it contains little to no organic material, making it more stable and compactable. That’s why it’s ideal for:
-
Raising low areas
-
Leveling sloped land
-
Supporting patios, roads, and building pads
-
Filling behind retaining walls
Step-by-Step: Calculating Fill Dirt on a Slope
Step 1: Measure the Slope Area
Start by collecting three basic measurements:
-
Length (L) – horizontal distance across the slope
-
Width (W) – left to right, perpendicular to the slope
-
Height (H) – vertical rise from bottom to top
If you’re leveling from the bottom to a flat top edge, you’re working with a triangular cross-section—basically a wedge.
Step 2: Use the Wedge Volume Formula
Use this formula to estimate the amount of fill dirt needed:
Cubic Feet = 0.5 × Length × Width × Height
Cubic Yards = (0.5 × L × W × H) ÷ 27
Example:
A slope that’s:
-
40 feet long
-
15 feet wide
-
4 feet high at the deepest point
Calculation:
(0.5 × 40 × 15 × 4) ÷ 27 = 1,200 ÷ 27 = 44.4 cubic yards
You’ll need about 44.4 yards of fill dirt before accounting for compaction.
Step 3: Account for Compaction
Fill dirt settles after it’s placed and compacted. To avoid falling short, increase your total based on a compaction factor.
Typical compaction allowances:
-
10–15% for screened fill
-
Up to 25% for loose or heavy clay soils
Formula:
Adjusted Volume = Raw Volume × (1 + Compaction Rate)
Example (15% compaction):
44.4 × 1.15 = 51.1 cubic yards
Order Fill Dirt the Easy Way
At Hello Gravel, we simplify the process from calculation to delivery. No chasing quotes. No back-and-forth. Just the right materials delivered directly to your site.
Get a Quote Today
We offer:
-
Clean, compactable fill
-
Honest pricing and fast delivery
-
No-stress online ordering
Measure the area → Let us handle the rest.
Author: Chance Kittrell