Concrete Volume Calculator

Calculate concrete volume in cubic metres for slabs and footings.

Slab Dimensions

Length (Feet)

Width (Feet)

Thickness (Inches)

Required Concrete Volume3.7 yd³Total Area: 300 sq ft (100 cu ft)

80 lb Premix Bags167 Bags

60 lb Premix Bags223 Bags

Guide & Educational Reference

How to Use the Concrete Volume Calculator

1Enter the project Length in Feet.
2Enter the project Width in Feet.
3Enter the slab or footing Thickness in Inches (note the mixed unit: thickness is in inches while length and width are in feet).
4View total surface area (sq ft), volume in cubic feet (cu ft), volume in cubic yards (Yards³), and premix bag estimates (80 lb and 60 lb bags).

Understanding Concrete Volume Calculations

The Concrete Volume Calculator estimates the 3D space (volume) required for rectangular concrete projects such as slabs, patios, driveways, footings, and pads. By converting mixed input units (feet and inches) into cubic feet and cubic yards, it provides standard ordering estimates for ready-mix delivery or bagged concrete.

Formulas Implemented by THE CALC

1. Mixed-Unit Thickness Conversion

Converts thickness from inches to feet.

Thickness (ft) = Thickness (in) / 12

2. Surface Area & Volume in Cubic Feet

Calculates rectangular surface area and 3D volume.

Surface Area (sq ft) = Length (ft) × Width (ft) | Volume (cu ft) = Area × Thickness (ft)

3. Volume in Cubic Yards

Converts cubic feet to cubic yards (1 cubic yard = 27 cubic feet).

Cubic Yards (yd³) = Volume (cu ft) / 27

4. Premix Bag Quantity Estimates

Uses built-in yield assumptions (0.60 cu ft per 80 lb bag; 0.45 cu ft per 60 lb bag).

80 lb Bags = CEILING(Volume / 0.60) | 60 lb Bags = CEILING(Volume / 0.45)

Practical Real-World Example

20 ft × 15 ft Slab with 4-Inch Thickness

Area = 20 × 15 = 300 sq ft
Thickness (ft) = 4 / 12 = 0.3333 ft
Volume (cu ft) = 300 × 0.3333 = 100.0 cu ft
Volume (Yards³) = 100.0 / 27 = 3.70 Yards³
80 lb Bags = CEILING(100.0 / 0.6) = 167 Bags
60 lb Bags = CEILING(100.0 / 0.45) = 223 Bags

→ Concrete Volume: 3.70 Yards³ (300 sq ft, 100.0 cu ft) | Bags: 167 (80 lb) or 223 (60 lb)

10 ft × 10 ft pad, 6 in thick

Thickness = 6/12 = 0.5 ft; Volume = 10 × 10 × 0.5 = 50 cu ft = 50/27 ≈ 1.85 yd³; 80 lb bags = CEILING(50/0.6) = 84

→ ≈ 1.85 yd³; 84 bags (80 lb) or 112 bags (60 lb)

4 ft × 4 ft footing, 12 in thick

Thickness = 1 ft; Volume = 4 × 4 × 1 = 16 cu ft = 16/27 ≈ 0.59 yd³

→ ≈ 0.59 yd³; 27 bags (80 lb) or 36 bags (60 lb)

Important Model Assumptions & Considerations

Net geometric calculation: The calculator computes the exact geometric volume based on the entered dimensions and does not automatically include a waste or spillage allowance.
Built-in bag yield assumptions: Bag counts are calculated using fixed internal yield figures (0.60 cu ft per 80 lb bag; 0.45 cu ft per 60 lb bag). Actual coverage may vary by concrete brand or mix formulation.
Site condition variance: Actual material requirements on a job site may differ due to uneven subgrade, form bowing, spillage, or over-excavation.
Rectangular prism geometry: Designed for flat rectangular slabs, pads, and footings; irregular or circular pours require separate calculations.

Frequently Asked Questions

Why is thickness entered in inches while length and width are in feet?

Concrete slabs are typically measured in feet for length and width, but specified in inches for depth or thickness. The calculator automatically converts inches to feet (dividing by 12) before computing volume.

How many cubic feet are in a cubic yard of concrete?

One cubic yard equals exactly 27 cubic feet (3 ft × 3 ft × 3 ft = 27 cu ft).

Does this calculator include a waste allowance?

No. The calculator returns the exact net geometric volume derived from the entered dimensions.

How are the premix bag counts calculated?

The net volume in cubic feet is divided by the yield per bag (0.6 cu ft for an 80 lb bag, 0.45 cu ft for a 60 lb bag) and rounded up to the next whole bag.