Concrete Volume Calculator: Free Online Concrete Estimator
Use our free concrete volume calculator to determine exactly how much concrete you need in cubic yards and cubic feet for slabs, pads, and footings. Designed for contractors, builders, and DIY homeowners, this tool calculates the precise volume from your length, width, and thickness measurements. Enter your dimensions to get instant, accurate volume results for ordering ready-mix or bagged concrete.
How to use this calculator.
- Measure your project area. Measure the length and width in feet. For L-shaped or irregular slabs, divide the area into rectangles and calculate each section separately.
- Enter the thickness. Input the slab thickness in inches. Patios and walkways are typically 4 inches. Driveways need 5-6 inches. Garage floors and commercial slabs need 6 inches or more.
- Review your results. The calculator displays volume in both cubic yards (the standard unit for ordering ready-mix) and cubic feet (useful for calculating bagged concrete quantities).
- Add a waste factor manually. Multiply the result by 1.05 to 1.10 to account for spillage, uneven subgrade, and form deflection.
How do you calculate concrete volume for slabs and pads?
Concrete volume is calculated from the rectangular dimensions and converted to cubic yards, the standard unit for ready-mix concrete orders.
Volume (cu ft) = Length (ft) × Width (ft) × Thickness (in) ÷ 12
Volume (cu yd) = Volume (cu ft) ÷ 27
Where:
- 324 is the combined conversion factor: 12 (inches to feet) × 27 (cubic feet to cubic yards).
- 1 cubic yard of concrete weighs approximately 4,000 lb (2 tons) and covers 81 sq ft at 4 inches thick.
- Always round up to the nearest 0.5 yard. Running short means a cold joint and a structurally compromised slab.
Example calculation.
Let's calculate the concrete volume for a garage floor.
Scenario: You are pouring a garage floor that is 24 ft long and 22 ft wide with a 6-inch slab thickness.
- Calculate cubic feet: 24 ft × 22 ft × 6 in ÷ 12 = 264 cu ft
- Convert to cubic yards: 264 cu ft ÷ 27 = 9.78 cu yd
Result: You need approximately 10 cubic yardsof concrete for this garage floor (rounded up to the nearest 0.5 yard). At $150 per yard for ready-mix, the concrete cost is approximately $1,500.
Tips from the field.
- Always round up to the nearest 0.5 yard. It costs far less to have a small amount of extra concrete than to call for a short-load delivery. A cold joint ruins a slab permanently.
- Measure your forms, not the ground. Concrete fills the forms, so measure the inside dimensions of your formed area. Warped or misaligned forms change the actual volume needed.
- Check subgrade levelness. Low spots in the subgrade consume extra concrete. A 1-inch low spot across a 20 ft by 20 ft slab adds 1.23 cubic yards of unexpected concrete.
- Know your minimum order. Most ready-mix suppliers have a 1-3 yard minimum. Orders below the minimum incur a short-load fee of $40-$80. For very small pours, bagged concrete may be cheaper despite the higher per-yard cost.
Disclaimer: This calculator provides estimates for planning purposes only. Actual concrete requirements vary based on subgrade conditions, form accuracy, and spillage. For structural slabs or load-bearing applications, consult a licensed structural engineer. PavementCalculator.com assumes no liability for material overages or shortages.
Cost, price, and density figures on this page reflect approximate U.S. averages as of August 2026 and vary by region, supplier, and material availability.
Frequently asked questions.
How do I calculate the volume of concrete I need?
Multiply length × width × thickness (inches ÷ 12), then divide by 27 for cubic yards. For a 10×10 ft slab at 4 inches: (10 × 10 × 0.333) ÷ 27 = 1.23 cubic yards. For cylindrical shapes: π × r² × height. Use our calculator: it handles all shapes.
What is a cubic yard of concrete?
A cubic yard is 3 ft × 3 ft × 3 ft = 27 cubic feet. It's the standard unit for ordering ready-mix concrete. One cubic yard weighs ~4,000 lbs and covers 81 sq ft at 4 inches thick. A standard concrete truck holds 8-10 cubic yards.
Should I order extra concrete?
Yes: order 5-10% extra for spillage, uneven subgrade, and form deflection. Running short mid-pour creates cold joints that compromise strength. For a 10-yard order, add 0.5-1 extra yard. Most ready-mix suppliers charge a small-load fee for orders under 5 yards.
What thickness of concrete do I need for a patio vs a driveway?
Patios/walkways: 4 inches. Driveways (cars): 4-5 inches. Driveways (trucks/RVs): 6 inches. Garage floors: 4-6 inches. Commercial loading docks: 6-8 inches. Always check local building codes for minimums.
How do I calculate concrete volume for a cylinder?
Volume = π × r² × height, where r = diameter ÷ 2 (in feet). For a 12-inch diameter, 4-ft column: π × (0.5)² × 4 = 3.14 cu ft ÷ 27 = 0.116 cu yd. Use our calculator: enter diameter in inches and height in feet for automatic calculation.