So how much concrete do you need?
If you’re calculating a square or a rectagle you need the length, width, and depth. You times them together. If your length is 20 metres, your width half a metre, and your depth 0.8 metres you would need (20×0.5×0.8=) 8 cubic metres.
To calculate a circle or cylinder you need the radius and the depth. To find the Radius you may need to measure the diameter and half it. You then need to square the Radius i.e. Radius x Radius and then times that by Pie (which is about 3.14). You need to times this figure by the depth. So if your Radius was half a metre you would times 0.5 x 0.5 and times that by 3.14 which equals 0.785. You then times 0.785 by the depth say 4 metres would mean you would need 3.2 cubic metres.
To calculate a triangular shape you need to measure two sides of the triangle and the depth. Times the three measurements together and divide by two.
If the sides of your triangle at 10 metres and 5 metres and your depth is 0.2 metres you calculate 10 x 5 x 0.2 to get 10 and then divide it by 2 so you would need 5 cubic metres of concrete.