Working out the volume of a box is no problem. If the box is (for example) 40 cm square and 45 cm high (these figures will become clear in a mo) then you just multiply length by width by height (LxWxH). So:

L x W: 40 x 40 = 1600 cm²

L x W x H: 40 x 40 x 45 = 72000 cm³

For ease of reference, turning that into litres which is what I want is simply dividing the result of L x W x H by 1000. Correct me (please!) if I’m wrong but I think this can be written as ((l*w*h)/1000). The result is 72 litres. Dandy.

Here’s my problem. This is the shape of my tank:

The grey shaded part is the tank. What I need to do is remove the yellow triangle volume from the square. Measurements are on the image above, height is the same as the tank at 45cm.

I just cannot for the life of me grasp how to work out the volume of the yellow shaded area. Anyone with more brains (and life-force) than me able to work out that volume? I know there’s something about 1/2 base x width x height or similar but I can’t find a good reference on the net (at 11.25 PM on Sunday night…)

On a related note I have added six new plants to the tank today – it was looking much bare. Picture is here (Photobucket link) taken with a Blackberry, I apologise for the quality!