How we calculate concrete
We convert thickness from centimetres to metres, multiply by length and width, add the margin and then use density to estimate kilograms and bags.
length Γ width Γ (thickness Γ· 100) Γ (1 + margin)
Density is an estimate
Density and yield vary by product and water content. The manufacturer data sheet takes priority over any generic value.
Do not ignore logistics
More than one hundred bags means a lot of weight, transport, storage and mixing time. Cost is not the only factor.