DIY
A shed base, a shim of a patio, a post footing. Get the volume right first and the rest of the job is arithmetic.
Concrete is sold and mixed by volume, so that is the number to nail. A 3 × 2 m base at 100 mm thick is the slab below — and geometry is worth opening if the shape is anything other than a rectangle.
A C20 mix is the usual choice for a domestic base. The tool converts volume into cement, sand and aggregate — and into whole bags, which is what you actually have to carry.
If the slab is holding a structure, the loads end up in bolts. The torque tool converts a bolt size and grade into the tightening torque that actually gives the clamp force you want.
Concrete does not dry, it reacts — and that reaction is temperature dependent. Cold slows it dramatically and frost during the first day can wreck the surface, so check what the air is actually doing.
Geometry sets the volume, the mix tool turns it into bags, bolt torque holds the thing down and the weather decides whether today is the day. Change the slab size and the whole chain re-costs itself.