Plaster
Wet volume is area × thickness. Multiply by about 1.27 for the dry loose volume (more mortar fills joints and surface hollows), add wastage, then split by the mix ratio. 100 m² of 12 mm plaster in 1:4 needs 1.2 × 1.27 × 1.05 = 1.60 m³ of dry materials: 461 kg of cement (10 bags) and 1.28 m³ of sand.
Tiles, adhesive and grout
Tiles per m² = 1/((L + j)(W + j)). Add 5–10% wastage (more for diagonal laying or small rooms), then round up to whole boxes. Adhesive is a rate per m² from the product sheet. Grout uses the standard formula kg/m² = (L + W)/(L × W) × tile thickness × joint width × 1.6.
Paint
Litres = area × coats ÷ coverage per coat. Emulsion typically covers 10–12 m²/L per coat on smooth plaster, less on rough or absorbent surfaces. Primer is usually one coat, and wall putty (if used) is about 1 kg/m² for two thin coats.
FAQ
Why 3.64 litres per gallon?
Paint in Pakistan and the Gulf is commonly sold in 3.64 L “gallon” tins. Divide the litres by 3.785 for US gallons.
Should I deduct openings?
Yes for large openings. Many estimators deduct only openings over about 0.5 m² for plaster and paint, since reveals and edges use extra material.