Hole Volume Calculator: Fill Material and Cost
Post holes and trenches are the quiet spend on most outdoor projects. Nobody budgets for them until the fence posts need concrete. This hole volume calculator works out how much space a round, square, or rectangular hole takes, then converts that volume into the weight of whatever’s going in: concrete, gravel, sand, soil, or mulch.
Enter the hole dimensions, set the depth and how many you’re filling, and pick a material. The tool applies that material’s density to give you pounds and kilograms, then works the cost from a price per cubic yard, foot, meter, or ton. Handy for fence lines, deck footings, mailbox posts, and garden beds.
How to Use the Hole Volume Calculator
Choose your currency from the top dropdown.
Pick the hole shape. Round covers most post holes.
Type the diameter or side length, then set the unit.
For rectangular holes, add the length in the second dimension field.
Enter the depth. Post holes usually sit 24 to 36 inches deep.
Set how many holes you’re filling.
Pick a material from the dropdown. Concrete, gravel, and soil each have their own density.
Adjust waste, then add your price per unit and any extra cost.
The Summary tab leads with total volume in cubic yards and cubic meters. Detailed Breakdown lists every value behind the result.
How the Hole Volume Calculator Formula Works
Volume is area times depth. The shape decides the area formula, and the depth does the rest.
Formula: Round volume = π × (Diameter ÷ 2)² × Depth
Formula: Square volume = Side × Side × Depth
Formula: Rectangular volume = Width × Length × Depth
Formula: Total volume with waste = Volume per hole × Count × (1 + Waste %)
Formula: Material weight = Volume with waste × Density
Densities come from the material dropdown. Concrete sits at 145 lb/ft³, gravel at 100, sand at 95, soil at 90, crushed stone at 105, water at 62.4, topsoil at 85, and mulch at 30. Pick Custom if you have a supplier’s exact number, and the density field becomes editable.
Cost depends on the pricing unit. Per cubic yard, per cubic foot, and per cubic meter scale with volume. Per ton scales with weight instead. That last option matters when you’re buying gravel or sand by the ton rather than by volume, which is how most bulk yards quote.
Worked Example: Six Fence Post Holes, 10 in Round by 30 in Deep
Say you’re setting six fence posts. Each hole is 10 inches wide and 30 inches deep. You’re filling with concrete at 145 lb/ft³. Waste factor is 5%. Price is $150 per cubic yard.
Diameter in feet: 10 ÷ 12 = 0.8333 ft
Radius: 0.4167 ft
Cross-section: π × 0.4167² = 0.5454 ft²
Depth in feet: 30 ÷ 12 = 2.5 ft
Volume per hole: 0.5454 × 2.5 = 1.364 ft³
Total base volume: 1.364 × 6 = 8.18 ft³
With 5% waste: 8.59 ft³, or 0.318 yd³
Concrete weight: 8.59 × 145 = 1,246 lbs (about 565 kg)
Cost at $150/yd³: 0.318 × 150 = $47.70
Under 50 dollars for the whole fence line, plus whatever the mix costs if you’re using bags. At 80 lb bags yielding 0.6 ft³ each, that’s about 15 bags. Six posts, 15 bags. That’s the number worth knowing before you load the truck.
