Concrete Calculator
Calculate the volume of concrete needed for slabs, footings, columns, and curbs. Computes cubic yards, cubic feet, 80lb/60lb bags, truckloads, and estimated cost.
Calculation Results
Total volume of ready-mix concrete needed, including waste allowance.
Total concrete volume measured in cubic feet.
Number of standard 80 lb bags (yields 0.60 cu ft mixed concrete each).
Number of standard 60 lb bags (yields 0.45 cu ft mixed concrete each).
Standard 10-cubic-yard ready-mix transit mixer truckloads.
Total estimated ready-mix concrete cost based on local yardage price.
Total wet concrete load weight (standard normal-weight concrete ~150 lbs/cu ft).
How This Calculator Works
Follow these professional contractor steps to estimate your pour:
- Select Shape: Choose between a flat slab (patio, driveway, footing), cylindrical pier (sonotube, post footing), or continuous curb.
- Measure In-Place Forms: Input the true interior dimensions of your wooden forms. You can toggle between inches, feet, yards, centimeters, or meters.
- Factor in Waste (5%–10%): An uneven subgrade, deflection in wood forms, or residual pump hose concrete will cause shortages if you calculate exact net volume. 10% is standard; use 15% for rough excavation.
- Review Takeoff: The tool instantly displays cubic yards for ready-mix orders, exact sack counts for retail bags, transit truckloads, and total weight.
Formula & Calculations
Concrete volume calculations determine the space occupied by geometric solids, adjusted for subgrade settlement, spillage, and form deflection according to American Concrete Institute (ACI 318) guidelines.
1. Volumetric Formulas by Geometry
- Rectangular Slabs & Footings:
Volume (cu ft) = Length (ft) × Width (ft) × Depth (ft) - Round Columns, Piers & Sonotubes:
Volume (cu ft) = π × (Diameter / 2)² × Depth (ft) - Curbs, Gutters & Barriers:
Volume (cu ft) = Length (ft) × Width (ft) × Height (ft)
2. Cubic Yard Conversion
Because ready-mix suppliers batch material by the cubic yard, divide total cubic feet by 27:
Cubic Yards = Cubic Feet / 27
3. Pre-Mix Bag Yields
When mixing on site with bagged concrete (ASTM C387), yields are calibrated by dry sack weight:
- 80 lb bag: Yields
0.60 cu ft(requires 45 bags per cubic yard) - 60 lb bag: Yields
0.45 cu ft(requires 60 bags per cubic yard) - 50 lb bag: Yields
0.375 cu ft(requires 72 bags per cubic yard) - 40 lb bag: Yields
0.30 cu ft(requires 90 bags per cubic yard)
4. Compressive Strength (PSI) Standards
- 2,500 PSI: Walkways, footpaths, and residential fence post footings.
- 3,000–3,500 PSI: Patios, shed pads, and residential driveways.
- 4,000+ PSI: Heavy vehicle driveways, commercial foundations, and freeze-thaw exposure.
Step-by-Step Calculation Examples
Backyard Patio Slab (12ft x 10ft x 4in)
Standard 4-inch thick concrete patio pour with 10% waste buffer and $140/yd material cost.
- shape: slab
- length: 12
- width: 10
- thickness: 4
- waste: 10
- cost_per_yard: 140
- volume: 1.63 cu yd
- volume_cuft: 44.0 cu ft
- bags_80lb: 74
- estimated_cost: $228.15
Pier Footings (Four 12in Sonotubes x 4ft Deep)
Four structural frost-line deck footings combined into an equivalent 16ft cylinder.
- shape: column
- diameter: 12
- height: 16
- waste: 10
- cost_per_yard: 140
- volume: 0.51 cu yd
- volume_cuft: 13.8 cu ft
- bags_80lb: 23
- estimated_cost: $71.68
Frequently Asked Questions
How much concrete is in a cubic yard?
One cubic yard of concrete equals 27 cubic feet. Visually, this is a 3ft by 3ft by 3ft cube. A single cubic yard will cover approximately 81 square feet at a standard 4-inch depth.
How many 80 lb or 60 lb bags make a cubic yard?
It takes 45 bags of 80 lb concrete mix, or 60 bags of 60 lb concrete mix, to make one cubic yard of placed concrete.
When should I order a ready-mix truck instead of mixing bags?
As a rule of thumb, if your project requires more than 1 cubic yard (45 eighty-pound bags), ordering a ready-mix delivery truck saves substantial labor and guarantees consistent PSI strength across the pour. For smaller projects under 1 yard, mixing bags on site is generally more economical.
How thick should a concrete slab be?
A standard residential walkway or patio should be 4 inches thick. For driveways supporting passenger vehicles, 4 to 5 inches is standard. For heavy trucks, RV pads, or industrial equipment, specify 5 to 6 inches reinforced with #4 rebar.
How far apart should concrete control joints be?
According to ACI standards, control joints should be spaced at a distance in feet equal to two to three times the slab thickness in inches. For example, a 4-inch thick slab should have control joints every 8 to 10 feet in both directions to prevent uncontrolled cracking.
How long does concrete take to cure?
Concrete reaches about 50% of its design strength within 3 to 7 days, and achieves its standard design strength (specified PSI) after 28 days. Keep the surface moist or apply a curing compound during the first 7 days for maximum durability.