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.

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 Guide

How to Use the Concrete & Square Footage Calculator: Practical Guide & Visual Analysis

Plan slabs, patios, driveways, and footings by computing exact geometric volume plus a customizable contractor wastage allowance (5%–15%). Whether you are researching concrete slab calculator, cubic yards calculator, square footage calculator, how many bags of concrete, 80lb concrete bag calculator, this interactive tool helps you calculate square footage, concrete volume in cubic yards and cubic meters, and the number of 80-lb or 60-lb pre-mix bags needed with a wastage buffer.

Interpreting the 3 Custom Visual Graphs & Key Outputs

As you adjust Slab Length, Slab Width, Slab Thickness / Depth, Number of Identical Slabs, the calculator immediately computes Total Volume in Cubic Yards (yd³) & Cubic Meters (m³), Total Surface Area (sq ft & m²), 80-lb Pre-Mix Bag Count, 60-lb Pre-Mix Bag Count and updates all three domain-specific SVG charts in real time. Instead of relying on a single static figure, you can inspect the primary domain diagram, component breakdown, and multi-point trajectory curve to see how changing your inputs shifts the final result. Use the Compare (up to 3 scenarios) button to evaluate side-by-side variations before making a decision.

Real-World Benchmark & Planning Tips (Global (US Customary & Metric))

In our benchmark scenario (20 ft × 12 ft Patio Slab at 4 Inches Thick with 10% Wastage), 3.26 yd³ (2.49 m³) or 147 bags (80-lb) / 196 bags (60-lb). Keep in mind that uses ASTM C387 standard pre-packaged dry concrete yields (0.60 ft³ per 80-lb bag, 0.45 ft³ per 60-lb bag). For related calculations in Construction & Home, explore Geometry Calculator (Right Triangle, Circle & Cylinder), Unit Conversion Calculator.