Foundation Calculator: Free Online Concrete Foundation Estimator
Use our free foundation calculator to estimate the concrete volume needed for your foundation slab and perimeter footings. Designed for general contractors, foundation specialists, and owner-builders, this tool calculates the slab volume, footing volume, and total concrete required for a monolithic slab-on-grade foundation in cubic yards. Enter your slab dimensions, slab thickness, footing width, and footing depth to get precise, ready-to-order concrete quantities instantly.
How to use this calculator.
- Enter your slab dimensions. Input the overall length and width of your foundation in feet. This represents the full footprint including any attached garage, porch, or patio that shares the same slab.
- Set your slab thickness. Standard residential slabs are 4 inches thick. Garage slabs and areas supporting heavy loads should be 5-6 inches. Enter the slab thickness in inches.
- Enter your footing dimensions. Input the footing width (typically 12-24 inches) and footing depth (typically 6-12 inches) in inches. The calculator automatically computes the linear footage of the perimeter footing.
- Review total concrete volume. The calculator sums the slab and footing volumes to give you the total cubic yards to order. Always round up to the nearest half-yard and add a 10% safety margin.
- Verify with your building department. Local codes specify minimum footing dimensions based on soil bearing capacity, frost depth, and building loads. Always confirm your calculated dimensions against code requirements before ordering.
How do you calculate foundation concrete volume and cost?
Foundation concrete volume is calculated as the sum of the slab volume and the perimeter footing volume. Each component is computed separately and then combined for the total.
Slab Volume (cu yd) = Length (ft) × Width (ft) × Slab Thickness (in) ÷ 324
Footing Perimeter (ft) = 2 × (Length + Width)
Footing Volume (cu yd) = Perimeter (ft) × Footing Width (in) × Footing Depth (in) ÷ 3,888
Total Volume (cu yd) = Slab Volume + Footing Volume
Where:
- 324 converts square-feet-area × inches-thickness to cubic yards. Derived from: 12 inches per foot × 27 cubic feet per cubic yard = 324.
- 3,888 converts linear-feet × inches-width × inches-depth to cubic yards. Derived from: 12 × 12 × 27 = 3,888.
- Perimeter assumes a simple rectangular foundation. For complex shapes, calculate the footing length manually and use that value directly.
- Monolithic pour means slab and footings are poured as one continuous placement. This is standard for slab-on-grade foundations.
Example calculation.
Let's calculate the concrete needed for a typical house foundation.
Scenario: You are pouring a monolithic slab-on-grade foundation for a 40 ft × 30 ft home with a 4-inch slab thickness, 16-inch wide footings, and 8-inch deep footings.
- Calculate slab volume: 40 × 30 × 4 ÷ 324 = 14.81 cu yd
- Calculate footing perimeter: 2 × (40 + 30) = 140 linear feet of footing
- Calculate footing volume: 140 × 16 × 8 ÷ 3,888 = 4.59 cu yd
- Calculate total concrete: 14.81 + 4.59 = 19.40 cu yd
- Add 12% waste factor for a foundation pour: 19.40 × 1.12 = 21.73 cu yd. Order 22 cubic yards.
Result: You need approximately 22 cubic yardsof concrete for this 1,200-square-foot foundation. This requires 2 full truckloads (a standard ready-mix truck holds 10-11 cubic yards). Coordinate the two trucks to arrive with no more than 30 minutes between them to avoid a cold joint.
Tips from the field.
- Schedule a foundation pour for early morning. Foundation pours are large and complex. Starting at 7 AM gives you the full day for placing, consolidating, screeding, floating, and starting the finishing process. Afternoon pours that run late risk finishing in the dark, which nearly always results in a poor-quality slab surface.
- Have at least 4-5 workers for a foundation pour. You need one person on the chute, two spreading and rodding the concrete, one on the vibrator, and one screeding. For pours over 15 cubic yards, add more workers or accept that the finish quality will suffer.
- Use a concrete pump for difficult access. If the truck cannot back right up to the forms, rent a concrete pump ($400-$600 for the day). Wheelbarrowing concrete across rebar and mesh is slow, exhausting, and produces inconsistent placement. A pump line places concrete exactly where you need it.
- Verify footing excavation before ordering concrete.Measure the actual footing trench depth and width at multiple points around the perimeter. Excavators rarely dig perfectly to plan, and over-excavation consumes significant extra concrete. Adjust your calculations based on actual measurements, not plan dimensions.
- Plan for the anchor bolts. Place foundation anchor bolts (1/2-inch diameter, 10-12 inches long) into the wet concrete within 30 minutes of screeding. Space them no more than 6 feet apart and within 12 inches of corners and ends. J-bolts must be set while the concrete is still workable: once it begins to stiffen, bolts cannot be properly set.
Disclaimer: This calculator provides estimates for planning purposes only. Foundation design must consider soil bearing capacity, frost depth, seismic requirements, and structural loads as specified by a licensed structural engineer and local building codes. Never pour a foundation based solely on calculator estimates. PavementCalculator.com assumes no liability for foundation failures, material overages, or structural deficiencies.
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 much concrete do I need for a foundation?
For a typical 2,000 sq ft house foundation (4-inch slab on 12-inch × 24-inch footings): the slab takes approximately 24.7 cubic yards, and the footings take approximately 18.5 cubic yards, totaling 43.2 cubic yards. This is about 3 full truckloads of ready-mix. Use our foundation calculator above for your exact dimensions.
How deep should a concrete foundation be?
Foundation depth depends on the frost line in your region. In warm climates (Florida, Texas), 12-18 inches below grade is sufficient. In cold climates (Minnesota, North Dakota), foundations must extend 48-60 inches below grade to below the frost line. Footings should bear on undisturbed soil or properly compacted fill. Always check local building codes: they specify minimum foundation depth.
What PSI concrete should I use for a foundation?
Residential foundations typically use 3,000-3,500 psi concrete. Garage and basement floors: 3,500-4,000 psi. Foundation walls: 3,500-4,000 psi. In areas with sulfates in the soil, Type II or Type V cement is specified. The ACI (American Concrete Institute) code 318 requires a minimum 2,500 psi for most residential foundation applications.
How do you calculate foundation concrete volume?
Calculate the volume of each component separately and sum them. For slab: length × width × thickness. For footings: perimeter × width × depth. For foundation walls: perimeter × height × thickness. Convert all dimensions to feet, then divide cubic feet by 27 to get cubic yards. Always add 10-15% for waste, form deflection, and uneven excavation.
How much does a concrete foundation cost?
Concrete foundation cost ranges from $5 to $25 per square foot depending on type. Slab-on-grade: $5-$10/sq ft. Crawl space foundation: $10-$18/sq ft. Full basement foundation: $15-$25/sq ft. These costs include excavation, formwork, concrete, reinforcement, and labor. A 2,000 sq ft home: slab foundation $10,000-$20,000; basement foundation $30,000-$50,000.
How much concrete do I need for a 2,000 sq ft foundation?
A 2,000 sq ft foundation (for example, 50 ft × 40 ft) with a 4-inch slab and 16"×8" perimeter footings requires approximately 34 cubic yards of concrete including a 12% waste factor. The slab accounts for about 24.7 cubic yards and the footings for about 7.4 cubic yards. At 3,500 psi, this pour requires 3 full truckloads of ready-mix concrete. Use our calculator above with your exact dimensions.
What is the difference between a slab-on-grade and a full basement foundation?
A slab-on-grade foundation consists of a concrete slab poured directly on prepared soil with thickened edges or integral footings at the perimeter. It is the most common foundation type in warm climates and costs the least. A full basement foundation includes concrete walls extending 8-10 feet below grade on top of footings, with a separate slab floor. Basements cost 2-3 times more than slab-on-grade but provide usable living or storage space below the house. Crawl space foundations fall between the two, with short stem walls elevating the house 2-4 feet above grade.
How deep should foundation footings be?
Footing depth is primarily determined by the frost line in your region and the soil bearing capacity. In warm climates with no frost depth (southern US), footings typically extend 12 inches below grade. In moderate climates (mid-Atlantic, Midwest), footings extend 30-42 inches deep. In cold climates (northern US, Canada), footings must extend 48-60+ inches below grade to remain below the frost line. Always check your local building code for the minimum frost depth in your jurisdiction.
How wide should foundation footings be?
Residential foundation footings for single-story construction are typically 12-16 inches wide. Two-story construction requires 16-24 inch wide footings. The footing width must distribute the building load so that the bearing pressure on the soil does not exceed the allowable bearing capacity (typically 1,500-2,000 psf for residential soils). A 16-inch-wide footing supports approximately 2,000-2,667 pounds per linear foot, which is adequate for most single-family residential construction.
What PSI concrete is required for foundations?
The International Residential Code (IRC) requires a minimum of 2,500 psi concrete for residential foundations. However, most contractors specify 3,000-3,500 psi for added durability and margin of safety. For areas with sulfate soils or freeze-thaw exposure, 3,500-4,000 psi with air entrainment (5-7%) is recommended. The small cost premium for 3,500 over 2,500 psi concrete (typically $10-15 per yard) is cheap insurance for your home's structural foundation.