Concrete calculator
Cement, sand, aggregate and water for any pour — enter the slab or footing dimensions (or a volume straight off a bar-chart) and pick the grade. Nominal mixes per IS 456 with the 1.54 dry-volume factor; quantities come out in m³, cft and tonnes, the three units your suppliers quote in.
The usual RCC grade for a house — slabs, beams, columns.
Member sizes are the engineer’s job
This page turns a known volume into materials. What thickness your slab should be, what size the columns are, where the beams run — that is structural design, and it must come from a licensed structural engineer. For what the building rules let you build at all, see the plot guides.
Common questions
How many cement bags per m³ of M20 concrete?
About 8 bags. M20's nominal mix is 1:1.5:3 — with the 1.54 dry-volume factor, 1 m³ of finished concrete takes roughly 8 bags (400 kg) of cement, 0.42 m³ of sand and 0.84 m³ of 20 mm aggregate. M15 (1:2:4) takes about 6.3 bags, M25 (1:1:2) about 11.
Which concrete grade for a house?
M20 is the standard RCC grade for residential slabs, beams and columns. M10–M15 serve as plain concrete beds under footings and flooring. IS 456 allows nominal (by-proportion) mixes only up to M20 — M25 and above call for a lab-designed mix, so treat the M25 proportion here as a budgeting figure.
How much concrete does a roof slab need?
Slab volume is simply area × thickness. A 5 inch (125 mm) slab over 1,000 sq ft (93 m²) is about 11.6 m³ — roughly 94 bags of cement, 4.9 m³ sand and 9.8 m³ aggregate in M20. Enter your slab size in the calculator for exact figures; the slab's thickness itself comes from the structural design.
How much water goes into concrete?
A water-cement ratio of 0.45–0.55 suits house work; the calculator uses 0.5, i.e. 25 litres per bag. More water makes concrete easier to pour but permanently weaker — extra water is the most common site mistake, not less cement.