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Construction calculator — concrete, rebar, paint, tiles, walls, plaster and quick take-off

Concrete

Volume = length × width × thickness; divide a thickness given in centimetres by 100. Ready-mix is sold by the cubic metre and delivered by mixer truck, and you pay for the truck, so 15.75 m³ from 10 m³ trucks means two deliveries. Add 3–5% waste for spillage and formwork tolerance.

For small jobs mixed by hand, one cubic metre of roughly C20 concrete takes about 300 kg of cement (six 50 kg bags), 0.50 m³ of sand, 0.75 m³ of gravel and 170 litres of water. Use ready-mix for structural elements — hand-mixed strength is inconsistent.

Rebar

Steel quantities come from the structural design; for budgeting, use kg per m³ of concrete: raft foundation ~80, strip foundation ~90, columns and shear walls ~110, beams ~120, slabs ~80, general average ~95 kg/m³. A floor with 40 m³ of concrete needs about 40 × 95 = 3,800 kg (3.8 t).

Bar weight grows with the square of the diameter: kg/m = ز ÷ 162 (Ø in mm). Ø8 = 0.395, Ø10 = 0.617, Ø12 = 0.888, Ø14 = 1.21, Ø16 = 1.58 kg/m. One hundred 12 m bars of Ø12 weigh 0.888 × 12 × 100 ≈ 1,066 kg.

Paint

Coverage depends on the surface: interior emulsion ~0.125, exterior ~0.17, ceilings ~0.11 kg per m² per coat. Paint needed = area × coverage × coats; two coats is standard. 100 m² of interior wall, two coats: 25 kg → one 20 kg and one 10 kg pack. Prime raw plaster and absorbent surfaces; coverage drops otherwise.

If you do not know the wall area, use the helper: room perimeter × ceiling height − doors and windows. 24 m perimeter, 2.7 m height, 5 m² of openings → 59.8 m².

Tiles

Tile count = area including waste ÷ area of one tile, rounded up. Waste depends on the layout: 10% straight, 15% complex with many cuts, 18% diagonal. For 20 m² of 60 × 60 tiles at 10% waste: 22 m² ÷ 0.36 m² = 62 tiles, 16 boxes of 1.44 m². Adhesive ~4.5 kg/m² (25 kg bags), grout ~0.7 kg/m². Order all tiles from one batch and shade number.

Walls

Pieces = area × pieces per m² × (1 + waste). The Turkish 19×19×13.5 hollow brick takes 25 per m², the 19×19×8.5 brick 25 per m², a 60×25 AAC block 7, a 39×19 pumice block 12.5. Mortar for brick is ~25 kg/m²; AAC uses a thin-bed adhesive at ~4–5 kg/m². Subtract door and window openings from the area.

Plaster and screed

Mortar volume = area × thickness. Typical thicknesses: interior plaster 2 cm, exterior 2.5–3 cm, floor screed 4–5 cm. Cement per m³ of mortar: base coat 250, finish coat 300, screed 350 kg. 100 m² of interior plaster at 2 cm is 2 m³ of mortar → 600 kg of cement (12 bags), ~2 m³ of sand, ~400 litres of water.

Quick take-off

Before there is a design, budget with per-m² rules of thumb for reinforced-concrete frame housing (total floor area over all storeys): concrete 0.38 m³/m², steel 34 kg/m², formwork 2.6 m²/m², brick walls 0.15 m³/m². A 150 m² two-storey house needs roughly 57 m³ of concrete, 5.1 t of steel and 390 m² of formwork. Soil class, storey count and seismic zone change these figures; final quantities come from the structural design.