Concrete & Square Footage Calculator

Estimate surface area (sq ft / m²), concrete volume (yd³ / m³ / ft³), and 60-lb or 80-lb pre-mixed bag counts.

Total Concrete Volume (Incl. Wastage)
3.26 yd³ (2.49 m³)
88 ft³ • 147 bags (80 lb) or 196 bags (60 lb)
Total Surface Area 240 sq ft (22.3 m²)
Volume in Cubic Feet 88 ft³
80-lb Pre-Mix Bags 147 bags
60-lb Pre-Mix Bags 196 bags
Inputs
feet (ft)
Length of slab or footing in feet.
feet (ft)
Width of slab or footing in feet.
inches (in)
Standard patio/sidewalk thickness is 4 inches; driveways are 5–6 inches.
slabs
Multiplier if pouring multiple identical pads.
%
Contractors typically add 5%–10% to prevent running short.
Results & Graph
Total Concrete Volume (Incl. Wastage)
3.26 yd³ (2.49 m³)
88 ft³ • 147 bags (80 lb) or 196 bags (60 lb)
Total Surface Area
240 sq ft (22.3 m²)
Volume in Cubic Feet
88 ft³
Includes 10% waste buffer
80-lb Pre-Mix Bags
147 bags
0.60 ft³ yield per bag
60-lb Pre-Mix Bags
196 bags
0.45 ft³ yield per bag

Net Volume vs. Wastage Allowance (ft³)

Breakdown of net geometric volume and safety buffer
Graph 1 • Isometric 3D Concrete Slab & Rebar Grid Schematic Includes waste allowance and wet concrete mass (150 lb/ft³)
Width = 10 ft Length = 20 ft • Depth = 4" Net Volume = 2.72 yd³ • Cubic Feet (+10%): 73.3 ft³ • Cubic Meters: 2.08 m³ • Wet Concrete Mass: ~11,000 lbs
Graph 2 • Pre-Mix Concrete Bag Counts (80 lb, 60 lb, 50 lb, 40 lb) Compare pallet counts across standard bag weights
80-lb Heavy-Duty Bags (0.60 ft³ yield/bag) 123 bags 60-lb Standard Bags (0.45 ft³ yield/bag) 163 bags 50-lb Fast-Setting Bags (0.375 ft³ yield/bag) 196 bags 40-lb Easy-Lift Bags (0.30 ft³ yield/bag) 245 bags
Graph 3 • Cubic Yards Required vs. Slab Thickness (3" to 8") 1 standard ready-mix transit truck holds 9–10 yd³
0 yd³ 2.9 yd³ 5.9 yd³ 3" Slab: 2.04 yd³ 2.0 3" Slab 4" Slab: 2.72 yd³ 2.7 4" Slab 5" Slab: 3.4 yd³ 3.4 5" Slab 6" Slab: 4.07 yd³ 4.1 6" Slab 8" Slab: 5.43 yd³ 5.4 8" Slab
Summary: Total concrete volume is 88 cubic feet (3.26 cubic yards).
Summary: A slab measuring 20 ft × 12 ft (240 sq ft) at 4 inches thick requires 2.96 net cubic yards. Including a 10% overage buffer for grade unevenness and spillage, order 3.26 yd³ (2.49 m³) of ready-mix concrete or 147 × 80-lb bags.
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Formula & Mathematical Methodology: Slab Volume & Pre-Mix Bag Yield Equations

Volume (yd³) = L × W × Depth (in)12 × (1 + Waste%)27
Area (ft²) = L × W × Qty; Vol (ft³) = Area × (Depth_in / 12) × (1 + Waste%); Vol (yd³) = Vol (ft³) / 27
  • 27 ft³/yd³: 1 cubic yard = 3 ft × 3 ft × 3 ft = 27 cubic feet
  • 0.60 ft³ / 0.45 ft³: Standard cured yield of one 80-lb bag (0.60 ft³) or 60-lb bag (0.45 ft³)

Rounding: Volumes round to 2 decimal places; pre-mix bag counts round up (`Math.ceil`) to whole bags.

Worked Example: 20 ft × 12 ft Patio Slab at 4 Inches Thick with 10% Wastage

Estimate ready-mix cubic yards and 80-lb bags for a 20×12 ft backyard patio.

  1. Surface area = 20 × 12 = 240 sq ft (22.3 m²).
  2. Net volume = 240 × (4 ÷ 12) = 80.0 cubic feet (2.96 yd³).
  3. With 10% buffer: 80 × 1.10 = 88.0 cubic feet = 3.26 cubic yards (or 147 × 80-lb bags).
Result: 3.26 yd³ (2.49 m³) or 147 bags (80-lb) / 196 bags (60-lb).

Frequently Asked Questions

When is it cheaper to order a ready-mix concrete truck instead of buying 80-lb bags?

Once a project exceeds roughly 1.5 to 2 cubic yards (68 to 90 bags of 80-lb concrete), ordering bulk ready-mix delivery is usually faster and more economical.

Construction & Home · Building Materials & Area Estimation

Concrete & Square Footage Calculator: inputs, method, and how to read the result

Estimate surface area (sq ft / m²), concrete volume (yd³ / m³ / ft³), and 60-lb or 80-lb pre-mixed bag counts.

Choose inputs for the case you are checking

The defaults are illustrative. Replace them with values for your case and keep the units shown beside each field.

  • Slab Length: Length of slab or footing in feet.
  • Slab Width: Width of slab or footing in feet.
  • Slab Thickness / Depth: Standard patio/sidewalk thickness is 4 inches; driveways are 5–6 inches.
  • Number of Identical Slabs: Multiplier if pouring multiple identical pads.

What the calculation includes

With the default values shown, Total Concrete Volume (Incl. Wastage) is 3.26 yd³ (2.49 m³). The calculation follows Slab Volume & Pre-Mix Bag Yield Equations; the formula and variable definitions above show how the inputs combine.

One-input check: With the other defaults held constant, changing Slab Length from 20 feet (ft) to 22 feet (ft) changes Total Concrete Volume (Incl. Wastage) from 3.26 yd³ (2.49 m³) to 3.59 yd³ (2.74 m³). This is a comparison inside the calculator's stated model, not a prediction.

Where to use caution

  • Uses ASTM C387 standard pre-packaged dry concrete yields (0.60 ft³ per 80-lb bag, 0.45 ft³ per 60-lb bag).
  • Does not include rebar, wire mesh, or crushed gravel sub-base volume.

Scope: Global (US Customary & Metric) Check the assumptions and limitations against your situation before relying on the estimate.

More in Construction & Home: Geometry Calculator (Right Triangle, Circle & Cylinder), Unit Conversion Calculator.