A concrete slab is 10 cm thick: why enter 0.10 m?
Length, width and thickness must use metres consistently to produce cubic metres. Thickness is a common source of very large quantity errors.
Concrete calculator →Calculate one rectangular slab
A slab measuring 5 m by 4 m with a thickness of 10 cm has a thickness of 0.10 m. Its geometric volume is 5 × 4 × 0.10 = 2 m³. Entering 10 as the thickness instead would produce 200 m³, one hundred times the intended volume. The unit converter can check the thickness before the dimensions are entered.
State the allowance separately
If this example assumes an additional allowance of 5%, the adjusted quantity is 2 × 1.05 = 2.1 m³. That percentage is an illustrative input, not a universal recommendation. Uneven ground, actual dimensions and placement conditions can affect the quantity needed. Confirm an appropriate ordering allowance with the supplier or responsible professional.
Volume is not structural design
The tool estimates a rectangular volume and the allowance entered. It does not determine a safe thickness, reinforcement arrangement, concrete strength or foundation design. Those require appropriate professional specifications. When ordering, confirm the mix requirements, delivery arrangements and measured site dimensions as well as the volume. A correct multiplication cannot validate an unsuitable slab design or compensate for an inaccurate site measurement.
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