concrete weigth calculation

The question

"nina, saiz apa yang kita perlu utk concrete m25 jadi 20kg?"
(Nina, on what size needed for the m25 concrete to become 20kg?)

So here is the do-how;

let say the concrete will be in rectangular shape. 

Method 1

1) find the volume of the concrete. 
let say we assume 6" x 6" x 6" ; 
in this case assume every size that you feel near to the weight value. 

2) volume of a rectangular : width x height x thickness = Ym^3
then the density of the concrete. (refer the mix design reference)
For the gred m25, we have 2414kg/m^3.

3) Then use this formula to find the weight in kg = density x volume.

Method 2

1) From the handout, we have know the density. 
Given weight = 20 kg
Given density = 2414

so find the volume, v = 20/2414 = ??

2) since we have know the volume, now assume the size of the concrete, depend on your design.

tips : Method 1 is easier. 
tips : check next post for the mix design references.