Use this Concrete Calculator to estimate the concrete required for rectangular slabs, patios, pads, walkways, footings, and similar pours. Enter the length, width, thickness, number of equal sections, and optional waste allowance.

Concrete Volume Formula

Volume = length × width × depth

For multiple equal sections:

Base volume = volume of one section × number of sections

To include extra concrete:

Total volume = base volume × (1 + waste percentage ÷ 100)

Common conversions:

• Cubic yards = cubic feet ÷ 27
• Cubic meters = cubic feet × 0.0283168
• Estimated bags = required volume ÷ yield per bag

Example

Suppose a slab is 12 ft long, 10 ft wide, and 4 inches thick, with a 10% waste allowance.

First convert the thickness:

4 inches ÷ 12 = 0.333 ft

Calculate the base volume:

12 × 10 × 0.333 = 39.96 ft³

Add 10%:

39.96 × 1.10 = 43.96 ft³

Convert to cubic yards:

43.96 ÷ 27 = 1.63 yd³

The project requires approximately 44 cubic feet, or 1.63 cubic yards, of concrete.

Important Notes

• Use consistent units or select the correct unit for every measurement.
• Measure the actual formwork and use the planned concrete thickness.
• Uneven ground, over-excavation, form movement, spillage, and measurement differences may increase the required volume.
• Bag yields vary by product and manufacturer. Check the yield printed on the bag before purchasing.
• Round bag estimates up to the next whole bag.
• Divide irregular projects into smaller rectangular sections and add their volumes together.

This calculator estimates material volume only. Structural slabs, foundations, driveways, and load-bearing footings may require approved dimensions, reinforcement, concrete strength, and professional design.

Sources

• American Concrete Institute — Concrete Craftsman Series
• QUIKRETE — Concrete Quantity and Bag Calculator