Spike's Calculators

# Donut Shape Concrete Calculator - Metric

Calculate the amount of concrete needed in cubic metres and cubic yards for a donut shaped footing or slab.
Note: this is a circular area with a circular hole on the inside, not a torus!!

To be able to calculate the concrete volume needed for this type of footing you need to know the outer diameter of the circle, the inner diameter and the required depth. ### Formula's used:

Total Area
`A = π * D²  ÷ 4`

where A is the area in square metres, π = 3.14159265358979, D = outer diameter of circle

Perimeter P = π * D ÷
where P is the perimeter in meters, π = 3.14159265358979, D = diameter of circle

Volume
`V = π * D² ÷ 4 * d`

where V is the volume in cubic metres, π = 3.14159265358979, D = diameter of circle, d = depth of slab in millimetres

Volume calculation example:
```outer diameter  = 20 metres
inner diameter  = 19 metres
depth of slab = 100 millimetres
3.14159265358979 * 20 *  20 ÷ 4 ( 100 ÷ 1000) =  31.4 cubic metres
3.14159265358979 * 19 *  19 ÷ 4 ( 100 ÷ 1000) = 28.4 cubic metres
31.4 -  28.4 =  3 cubic metres of concrete needed for this footing```

To convert cubic metres to cubic yards multiply cubic metres * 1.31
To convert cubic metres to cubic feet multiply cubic metres * 35.32
To convert cubic yards to cubic feet multiply cubic yards * 27

### Donut Shape Concrete Footing/Slab - Metric

Outer Diameter m
Inner Diameter m
Depth mm

Width of Footing m
Surface Area of Footing
Inner Perimeter m
Outer Perimeter m
Total Length of Perimeter m

Cubic Metres
Cubic Yards yd ³
Cubic Feet ft ³

#### Calculation

1. enter the outer diameter in metres
2. enter the inner diameter in metres
3. the required depth in millimetres

#### Results

1. width of footing or slab in metres
2. square metres of this area (in case it is a slab)
3. inside perimeter in metres
4. outside perimeter, the circumference in metres
5. combined perimeter the outside plus the inside added together
6. concrete needed in cubic metres
7. concrete needed in cubic yards
8. amount of concrete needed in cubic feet

### When Ordering Concrete

This concrete calculator will help you in estimating the amount of concrete needed for your project. The amount given as needed, does not include any waste. It is recommended, depending on the job you are doing, to add anywhere from an extra 4% to 10% to your concrete order to make sure you have enough concrete to finish the job. Ask when ordering the concrete. They will be able to give you a good idea of what is needed.