How do I choose the right concrete grade (M15, M20, M25) for my structure?

Grade selection depends on the structural element and load it carries; footings and lower-load elements sometimes use a leaner mix, while columns, beams and slabs typically need M20 or higher depending on your structural engineer's design. The calculator lets you select a grade to see how it affects material proportions and cost, but the actual grade for each element of your building should come from your structural drawings, not a general assumption applied uniformly across the whole house.