How many premixed bags of Blue Circle Southern Cement Concrete Mix do I need? As a guide, the following formula will calculate how many 20 kg bags you will need:
1. Multiply to find your volume:
length ____ m x width ____ m x depth ____ m
= ____ m³ ( your volume )
2. Multiply your volume by 108*:
your volume ____ m³ x 108* = _____ bags of
20kg Blue Circle Southern Cement Concrete Mix required.
* 108 x 20kg bags of Blue Circle Concrete Mix will fill 1 cubic metre (m³).
For example:
Cubic Metres (m³)
.02
.04
.06
.08
.10
No. 20kg bags
2
4
6
8
10 *
* 108 x 20kg bags of Blue Circle Concrete Mix will fill 1 cubic metre (m³).
Note: For jobs over 1 cubic metre you may wish to consider ordering readymixed concrete from a concrete supplier. Click here to go to Boral Concrete»
1. First calculate the area: Area square metres (m²) = length x width (metres) 2. Then use the following table:
Cubic metres (m³) needed
Slab thickness in mm
Area (m²)
50
75
100
125
150
5
0.4
0.4
0.6
0.8
0.8
10
0.6
0.8
1.0
1.4
1.6
15
0.8
1.2
1.6
2.0
2.4
20
1.0
1.6
2.0
2.6
3.0
25
1.4
2.0
2.6
3.2
3.8
30
1.6
2.4
3.0
3.8
4.6
35
1.8
2.6
3.6
4.4
5.4
40
2.0
3.0
4.0
5.0
6.0
45
2.4
3.4
4.6
5.8
6.8
50
2.6
3.8
5.0
6.4
7.6
Yellow area: When using premixed bagged concrete as a guide 1 cubic metre (m) requires 108 x 20kg bags. Blue area: 1 cubic metre (m³) of concrete contains roughly 2.5 tonnes of raw material. Non-trades customers with jobs that fall into the blue shaded area might wish to consider ordering premixed concrete from a ready-mixed supplier.
How many bags of Blue Circle Southern Cement Post Hole Mix do I need? As a guide, the following formula will calculate how many 20 kg bags you will need:
1. Firstly, calculate the volume of the hole the post will go in:
Use the formula: V = Π r² h
radius of the hole x radius of the hole = ____ (r²)
3.142 (Π) x ____ (r²) x ____ m (depth of the hole) = ____ m³
(volume of the hole)
2. Now calculate the volume of the post using the same formula:
radius of the post x radius of the post = ____ (r²)
3.142 (Π) x ____ (r²) x ____ m (length underground) = ____ m³
(volume of the post)
3. Subtracting the volume of the post from that of the hole, we get:
____ m³ (volume of the hole) - ____ m³ (volume of the post) = ____ m³
(volume of cement required)
4. Multiply your volume by 108*:
(volume of cement required) ____ m³ x 108* = _____ bags of 20kg Blue Circle Southern Cement Post Hole Concrete required.
* 108 x 20kg bags of Blue Circle Post Hole Concrete will fill 1 cubic metre (m³).
1 / 2 / 3 
1 / 2.5 / 4 
1 / 3 / 5 
Yellow area: When using premixed bagged concrete as a guide 1 cubic metre (m) requires 108 x 20kg bags.
Blue area: 1 cubic metre (m³) of concrete contains roughly 2.5 tonnes of raw material. Non-trades customers with jobs that fall into the blue shaded area might wish to consider ordering premixed concrete from a ready-mixed supplier. 
