Construction & HomeCubic Yards = (Length_ft × Width_ft × Thickness_in / 12) / 27

Concrete Volume & Bags Calculator

Estimate required concrete cubic yards, cubic meters, and pre-mixed bag counts (40lb, 50lb, 60lb, 80lb) for slabs, footings, and cylindrical sonotubes.

Concrete Volume & Bag Solver

Cubic yards • Bag counts • Waste factor

Presets:

1. Structure & Dimensions

Structure Type

Length

Width

Thickness

Quantity

Waste Factor (%)

2. Concrete Volume NeededIncludes Waste

Total Volume

3. Pre-Mix Bag Estimates

80-lb Pre-Mix Bags (0.60 cu ft/bag)61 Bags

60-lb Pre-Mix Bags (0.45 cu ft/bag)82 Bags

50-lb Pre-Mix Bags (0.375 cu ft/bag)98 Bags

Estimated Total Cured Weight5,510 lbs (2.75 tons)

Formulas, calculation steps & FAQs below↓

Formulas & Calculation Guide

Estimating Concrete for Slabs, Footings & Columns

Concrete is purchased by volume, measured in Cubic Yards in the United States or Cubic Meters (m³) globally. One cubic yard is equal to a 3-foot cube (27 cubic feet), which weighs approximately 4,000 pounds (2 US tons).

Formulas by Project Type

Rectangular Slabs, Patios & Footings: Volume (cu yd) = (Length_ft × Width_ft × (Thickness_in / 12)) / 27
Round Columns, Pier Holes & Sonotubes: Volume (cu yd) = (π × (Diameter_in / 24)² × Height_ft) / 27
Concrete Steps & Stairs: Divide the staircase into individual rectangular step prisms, calculate each step’s volume, and sum them together: Total Volume = Sum(Step Width × Step Run × Cumulative Step Height)

Concrete slab – calculation example

Let’s estimate the concrete needed for a typical 12 ft by 12 ft patio slab that is 4 inches thick:

First, enter the slab length: length = 12 ft.
Enter the slab width: width = 12 ft.
Enter the thickness: thickness = 4 inches.
The calculator provides the exact volume: volume = 1.78 cubic yards (48 cu ft).
Adding a standard 10% safety margin: recommended order = 1.96 cubic yards.
If using bagged premix: you will need 89 bags (60-lb) or 67 bags (80-lb).

💡 Always order at least 10% extra concrete to account for uneven ground excavation, form deflection, and minor spillage.

Pre-Mixed Bag Requirements Breakdown

Bag Weight	Yield per Bag	Bags Needed per Cubic Yard	Bags Needed per Cubic Meter
40-lb Bag	0.30 cu ft (0.0085 m³)	90 bags	118 bags
50-lb Bag	0.375 cu ft (0.0106 m³)	72 bags	95 bags
60-lb Bag	0.45 cu ft (0.0127 m³)	60 bags	79 bags
80-lb Bag	0.60 cu ft (0.0170 m³)	45 bags	59 bags

Frequently Asked Questions

Expert answers to common calculations, unit conversions, and dimensional requirements.

How many cubic feet are in one cubic yard of concrete?↓

There are exactly 27 cubic feet in one cubic yard (3 ft × 3 ft × 3 ft = 27 cu ft).

How many 80-pound or 60-pound bags of concrete make one cubic yard?↓

One 80-pound bag yields approximately 0.60 cubic feet of mixed concrete; it takes 45 bags (80 lb) to make one cubic yard. One 60-pound bag yields approximately 0.45 cubic feet; it takes 60 bags (60 lb) to make one cubic yard.

How much extra concrete waste should I order?↓

Always add 10% extra margin for slabs, driveways, and footings to account for uneven grade excavation, form deflection, ground settlement, and spillage. For irregular deep footings or rocky trenches, order 15% extra.

What is the formula to calculate concrete for a 4-inch patio slab?↓

For a slab measuring length L (ft) and width W (ft) at 4 inches thick (4/12 = 0.333 ft): Volume (cu yd) = (L × W × 0.333) / 27 = (L × W) / 81. For a 10x10 ft patio: 100 / 81 ≈ 1.23 cubic yards (or ~1.35 yards with 10% waste).