Volume formulas
Concrete Volume Formulas for Five Shapes
Slabs, square footings and walls: volume = length × width × thickness. This also helps estimate concrete for patios, driveways and rectangular pads when the cross-section is uniform.
Round holes, columns and footings: volume = π × (diameter ÷ 2)2 × height. Circular slabs and tubes: volume = π ÷ 4 × (outer diameter2 − inner diameter2) × height. Use equal units for every dimension.
Curb and gutter: combine the model's two non-overlapping rectangular cross-sectional areas and multiply by length. Solid stairs: volume = width × [tread run × riser height × n(n−1) ÷ 2 + platform depth × total rise], multiplied by quantity. The top landing is counted separately.
Questions and assumptions
How do I calculate concrete for a slab or footing?
Choose Slabs, Square Footings, or Walls. Multiply length by width by thickness, using consistent units; the calculator converts between cubic units.
How much concrete is in a 10 ft × 10 ft × 4 in slab?
The geometric volume is about 33.33 cubic feet, or 1.23 cubic yards (0.94 cubic meters), before allowance. A real order may need additional material.
How do I calculate concrete for a round column?
Use π × (diameter ÷ 2)² × depth/height. For multiple columns, multiply by the quantity.
How do I calculate concrete for a circular tube?
The calculator subtracts inner circular area from outer circular area and multiplies by length/height. Inner diameter must be smaller than outer diameter.
What formula is used for curb and gutter?
The model adds a rectangular curb cross-section and a non-overlapping rectangular gutter cross-section, then multiplies by the run length.
How do the solid-stairs calculations work?
The current model sums riser sections beneath the treads and treats the upper landing separately. It assumes solid concrete, not hollow stairs.
Does the concrete calculator include waste?
The optional extra allowance increases the shown volume, weight and bag-weight equivalents. Real site allowances depend on conditions.
Do the 60-lb and 80-lb figures tell me exactly how many bags to buy?
No. They are theoretical weight equivalents from an assumed density of 2,130 kg/m³. To purchase bagged mix, divide volume by the manufacturer’s yield per bag and round up to whole bags.
Related calculators
Planning and safe use
Concrete Calculator in Cubic Yards, Cubic Feet and Cubic Meters
Enter your project measurements in meters, centimeters, feet or inches. The calculator converts the volume to ft³, yd³ and m³. One cubic yard equals 27 cubic feet; one cubic meter is approximately 35.315 cubic feet. The optional extra allowance is applied to all displayed volume and weight estimates.
Example slab: a 10 ft × 10 ft × 4 in slab needs approximately 33.33 ft³, 1.23 yd³ or 0.94 m³ of geometric volume before additional allowance. Check measurements and the real slab shape before ordering.
Concrete Bag Calculator: Weight Equivalents Versus Actual Yield
The result panel calculates a weight estimate using 2,130 kg/m³ (approximately 133 lb/ft³) and shows 60-lb and 80-lb weight equivalents. These values are not the same as the number of bags to purchase. Bagged concrete has a manufacturer-specified cured-volume yield; for example, a typical 60-lb QUIKRETE Concrete Mix bag yields about 0.45 ft³ and an 80-lb bag about 0.60 ft³. Divide required cubic feet by the yield stated on the actual product, then round up to whole bags.
Source: QUIKRETE Concrete Mix 1101 data sheet — published yields. Other manufacturers and concrete mixes may have different yields and densities.
Measurement and Project Assumptions
The drawings are illustrations, not engineered details. The calculation models uniform solid shapes and the specific curb/stair geometry in the input form; it does not size structural elements or account automatically for slopes, openings, hollow spaces, formwork tolerances or reinforcement displacement. Check project drawings and site conditions with the responsible engineer or contractor.