Concrete Calculator for the DIY slab builder

Finding a concrete calculator on the net is not difficult. They give the DIY concretor easy access to slab calculations, which must be done before pouring a concrete slab.

Trouble is they don't help with footing calculations. In fact they seem to assume you don't have footings!! A halfway decent concrete slab calculator will calculate the concrete required for a house slab and the footings. To do this, the job must be divided into components. See the graphic below.

  • Component 1 is the top slab
  • Components 2 and 5 are the side footings
  • Components 3 and 4 are the triangle form footings
  • Component 7 is the front and rear footings
  • Components 6 and 8 are the triangle forms for the front and rear footings
  • Components 9 and 10 are the widths (cross section) of the front and rear component 7
Concrete claculation template

This concrete calculator is a sort of calculus that you may have dabbled in at school, only easier. You will need a calculator and a pad to write the initial measurements. There are four steps to this process. Each step requires a result that must be written down, then the four results added. For a concrete yardage calculator, just swap the metre amounts for yard amounts...too easy.

Tip Before you start, do a rough estimate so can compare, e.g. if the top slab will be 14m x 7m x 200mm + footings = 19.6 cubic metres + a few more metres. For your information...a truck load is between 5-7 cubic metres. That's about 5 trucks, at $2-300/cubic metre(au). Ok lets begin the maths.

Step one
Calculate the volume of the top slab (component 1) length x width x height


Step two
Calculate the volume of the square footings (components 2+5) length x width x height x 2


Step three
Calculate the volume of the footing triangle forms (components 3+4)length x width x height - there are two and they are approx. half a square each so together they are a square!


Step four
Now add the forward and rear footings (components 6, 7 and 8) x2. Same again-length x width x height, with the width (components 9 and 10). Remember the triangles are half of a square.

Ok, so we have a result. If you speak to the concrete merchant he will advise an 'overage' amount to be added in case of under-calculation. Always overestimate as the cost of the truck coming back with a small amount is high. Our next page is a guide to pouring concrete .

Have a look at my concrete slab pictorial here

Or you can go back from Concrete calculator to Concrete Footing Design

Or go to Kithomebasics home page