The Concrete Calculator estimates how much concrete a simple slab, continuous footing, or round column needs. Enter finished dimensions in feet and inches, choose a waste allowance, and the tool shows base volume, total cubic feet, cubic yards, liters, and a rounded-up count for 40-, 60-, or 80-pound ready-mix bags. Calculations run locally in your browser.
How to use the concrete calculator
- Choose Rectangular slab or pad, Continuous footing, or Round column or pier.
- Enter the finished inside dimensions shown for that shape. Slabs use length and width in feet plus thickness in inches; footings use length in feet plus width and depth in inches; columns use diameter in inches and height in feet.
- Set a waste allowance. The default 10% is a planning allowance, not a universal requirement.
- Select the bag yield printed on your ready-mix product, then read the total volume and whole-bag estimate.
The result is an estimate for a regular, solid shape. It does not subtract embedded posts, openings, reinforcement, slopes, or irregular excavation. Measure the actual project and confirm the supplier’s product yield before buying material. For general geometry and unit conversions, use the area and volume calculator and US unit converter.
Formulas
The calculator converts all dimensions to feet and calculates volume in cubic feet.
Slab volume = length × width × thickness
Footing volume = length × width × depth
Round column volume = π × (diameter ÷ 2)² × height
Total volume = base volume × (1 + waste allowance ÷ 100)
Cubic yards = total cubic feet ÷ 27
For the bag result, the calculator divides total cubic feet by the selected nominal yield and rounds upward. Its built-in estimates are 0.30 ft³ for a 40 lb bag, 0.45 ft³ for a 60 lb bag, and 0.60 ft³ for an 80 lb bag. These are convenient planning values; packaging and mix designs can differ.
Worked examples
12 ft × 10 ft patio slab, 4 inches thick
Base volume is 12 × 10 × (4 ÷ 12) = 40 ft³. With a 10% allowance, the total is 44 ft³, or about 1.63 yd³. At a nominal 0.60 ft³ per 80 lb bag, round 44 ÷ 0.60 up to 74 bags.
40 ft continuous footing, 16 in wide and 8 in deep
Convert width and depth to feet: 16 in = 1.333 ft and 8 in = 0.667 ft. Base volume is approximately 40 × 1.333 × 0.667 = 35.56 ft³, or 1.32 yd³ before any allowance.
Round pier, 18 in diameter and 8 ft high
Diameter is 1.5 ft, so radius is 0.75 ft. Volume is π × 0.75² × 8 ≈ 14.14 ft³. Add the chosen allowance only after calculating this base value.
Scope and limits
This calculator is for early material planning, not an engineered design, structural approval, or a delivery order. It assumes level, constant dimensions and does not account for local building requirements, strength specifications, site conditions, forms, or placement method. Concrete is heavy and construction work can create safety risks; follow local rules, product instructions, and advice from a qualified professional for the actual project.
Authoritative references
The unit conversions in this tool follow the standard relationships behind the calculation: one yard is three feet, so one cubic yard is 3 × 3 × 3 = 27 cubic feet. For the underlying U.S. customary and SI conversion factors, see the National Institute of Standards and Technology (NIST) Guide for the Use of the International System of Units. The tool uses these fixed relationships when presenting cubic feet, cubic yards, and liters; it does not estimate a concrete mix design.
For real construction work, the calculation is only one planning step. The Occupational Safety and Health Administration’s concrete construction standard addresses workplace requirements and hazards that this calculator cannot evaluate. Confirm structural, mix, placement, and local-code decisions with the appropriate qualified professional or authority.