Rectangular volume

V = l × w × h

For a 5 m × 4 m × 0.1 m slab, the volume is 2 m³. A waste allowance changes the order quantity, not the geometric volume. To include 10% extra, multiply 2 by 1.1 to obtain 2.2 m³.

Convert all dimensions before multiplying. A depth of 10 centimetres is 0.1 metres, not 10 metres. Irregular shapes need subdivision or a different model.