Hole Volume Calculator
Calculate exactly how much concrete or fill material you need for round or rectangular holes. Enter dimensions in inches, number of holes, and choose your waste factor. Get volume per hole and total volume in cubic feet and cubic yards, plus concrete bag counts for 40-lb, 50-lb, 60-lb, and 80-lb bags, wet and dry weight, and estimated cost. Perfect for fence posts, deck footings, building foundations, and pier holes.
Diameter of the round hole
Length for rectangular holes; also used as hole depth for round holes
Width for rectangular holes
How deep the hole goes
How many identical holes (for fence posts, footings)
Extra concrete for spillage, uneven holes, and over-excavation
How do I calculate the volume of a hole?
For round holes: Volume = π × r² × d, where r = radius (half diameter) and d = depth. For rectangular holes: Volume = L × W × D. Convert all measurements to feet first. One cubic yard = 27 cubic feet. Standard concrete bag: 80-lb bag = 0.6 cu ft, 60-lb bag = 0.45 cu ft. Always account for a waste factor of 10-15% for spillage and over-excavation. For fence posts, the hole is typically 3× the post diameter.
How much concrete do I need for a fence post hole?
A typical fence post hole is 8-12 inches in diameter and 24-36 inches deep (below frost line). For a 4×4 post: dig a 10-inch diameter hole, 30 inches deep. Volume = π × (5/12)² × (30/12) = 1.36 cu ft. With 10% waste: 1.5 cu ft. That is 2.5 bags of 60-lb concrete or 2 bags of 80-lb per post. For 20 fence posts: 30 bags of 80-lb concrete. Allow the concrete to cure 24-48 hours before attaching fence panels.
What is the standard size for a concrete footing hole?
Standard footing sizes by structure: Deck posts: 12-16 inch diameter, 36-48 inches deep. Porch columns: 18-24 inch diameter, 36-48 inches deep. Building columns: 24-36 inch square, 48+ inches deep (below frost line). Fence posts: 8-12 inch diameter, 24-36 inches deep. The footing must extend below the frost line in your area (check local building code). Minimum footing size is typically 12 inches wide and 12 inches deep for light structures.
How do I convert hole volume to concrete bags?
Concrete bag yields: 80-lb bag = 0.6 cu ft. 60-lb bag = 0.45 cu ft. 50-lb bag = 0.375 cu ft. 40-lb bag = 0.3 cu ft. Formula: Number of bags = (Volume in cu ft × waste factor) ÷ yield per bag. For a 2 cu ft hole with 10% waste: 2 × 1.1 = 2.2 cu ft needed. Using 80-lb bags: 2.2 ÷ 0.6 = 3.67 → buy 4 bags. Using 60-lb bags: 2.2 ÷ 0.45 = 4.89 → buy 5 bags. Always round up to the nearest bag.