I've just updated the Concrete Calculator on blocklayer.com

http://www.blocklayer.com/concretecalculator.aspx

The biggest problem with concrete slab calculators is determining (entering) the shape.
So now, you can enter side lengths and click direction arrow buttons to draw pretty much any (straight sided - square cornered) shape you like.
Enter edge beam width and depth, and internal thickening length, width and depth to add volume for thickenings.

To see how it works, click the big green 'Demo' button and it will auto walk through drawing a shape and calculate the concrete volume and shape area.

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