Spike's Calculators

Calculate the amount of concrete you need in cubic feet and yards for a footing or slab in the shape of a donut.

Note: this is a circular area with a circular hole on the inside, not a torus!!

To calculate the concrete volume needed for this type of slab, you need to know the outer diameter of the circle, the inner diameter, and the required slab depth.

A = π * D² ÷ 4 where A is the area in square feet π = 3.14159265358979 D = outer diameter of the circle

P = π * D ÷ where P is the perimeter in feet p = 3.14159265358979 D = diameter of the circle

V = π * D² ÷ 4 * (d ÷ 12) where V is the volume in cubic feet p = 3.14159265358979 D = diameter of circle d = depth of slab in inches

outer diameter = 24 feet inner diameter = 22 feet depth of slab = 4 inchesCalculate the total volume first, then the inside area volume, and subtract this from the total volume;

3.14159265358979 * 24 * 24 ÷ 4 * ( 4 ÷ 12) = 150.796

The donut's total volume is 150.796 cubic feet.

The inner area's volume;

3.14159265358979 * 22 * 22 ÷ 4 * ( 4 ÷ 12) = 126.711

The volume of the inner circle is 126.711cubic feet

Subtract the inner volume from the total volume:

150.796 - 126.711 = 24.1

You need 24.1 cubic feet of concrete for this footing.

To convert cubic feet to cubic yards multiply cubic feet * 0.037037037037037

To convert cubic feet to cubic metres multiply cubic feet * 0.028316846592

To convert cubic yards to cubic metres multiply cubic yards * 0.764554857984

- enter the outer diameter in feet and inches
- enter the inner diameter in feet and inches
- the depth in inches

- footing or slab width in inches
- square footage of this area. (the surface area of the footing or slab)
- inside perimeter in lineal feet
- outside perimeter in lineal feet
- combined perimeter the outside plus the inside in lineal feet
- amount of concrete needed in cubic feet
- concrete needed in cubic yards
- concrete needed in cubic metres

- Circle
- Circle - Metric
- Donut
- Donut - Metric
- Ellipse
- Ellipse - Metric
- Equilateral Triangle
- Equilateral Triangle - Metric
- Octagon
- Octagon - Metric
- Oval
- Pentagon
- Pentagon - Metric
- Scalene Triangle
- Scalene Triangle - Metric
- Stadium Shape
- Stadium Shape - Metric
- Trapazoid
- Trapezium
- Plastic Concrete Footing Form