Concrete Calculator
Calculate cubic yards of concrete needed for slabs, footings, columns, and walls. Get bag counts and cost estimates.
How It Works
This calculator converts your project dimensions into cubic yards of concrete and tells you how many bags you need if mixing by hand.
Slab/Footing formula: Cubic Yards = (Length ft × Width ft × Depth in / 12) / 27 × (1 + Waste%).
Column formula: Cubic Yards = (π × (Diameter in / 2)² × Height in) / 46,656 × (1 + Waste%). The number 46,656 converts cubic inches to cubic yards.
Bag estimates: One 80 lb bag yields about 0.6 cu ft of mixed concrete. One 60 lb bag yields about 0.45 cu ft. Counts are rounded up so you never come up short.
Cost estimates use the typical ready-mix range of $130-$160 per cubic yard delivered.
Frequently Asked Questions
How many bags of concrete do I need?
First calculate the cubic yards needed using length, width, and depth. Then convert: one 80 lb bag covers about 0.6 cubic feet, and one 60 lb bag covers about 0.45 cubic feet. There are 27 cubic feet per cubic yard. This calculator handles the conversion and rounds up so you always have enough.
How much does a cubic yard of concrete cost?
Ready-mix concrete typically costs $130-$160 per cubic yard delivered, depending on your location and the mix design. Short-load fees may apply for orders under 5-10 yards. Bagged concrete is more expensive per yard but practical for small pours under 1 yard.
How thick should a concrete slab be?
A standard residential slab (patio, walkway, shed pad) is 4 inches thick. Driveways should be at least 5-6 inches. Garage slabs are typically 4-6 inches. For heavy loads or commercial use, 6-8 inches or more may be required with engineering.
What is a waste factor and how much should I add?
A waste factor accounts for spillage, over-excavation, uneven subgrade, and form irregularities. For most residential projects, 10% extra is standard. For complex shapes or rough subgrade, use 15-20%. It is always better to have a little extra than to run short mid-pour.
How do I calculate concrete for a round column or post?
Use the column/cylinder formula: Volume = pi x (diameter/2)^2 x height. Enter the diameter and height in this calculator and it handles the math, converting to cubic yards and bag counts automatically.