Estimation, Costing and Material Calculation
Estimation questions test measurement rules, conversion from area to litres and kilograms, and a defensible rate build-up.
Measurement rules
- Painting is measured in square metres of finished surface, length x breadth; mouldings and beads by girth.
- Following IS 1200 (Part 13) practice, openings up to 0.5 sq m are not deducted; larger openings are deducted; reveals and edges are measured separately; door shutters are taken on both faces plus edges.
- Walls, ceilings and different finishes are measured as separate items, and each scheduled coat can be a separate item.
Rate build-up
Material (coverage from the label plus 5-10 percent waste) + labour (output in sq m per day) + access and scaffolding + tools + overheads + profit + GST. Estimate = quantity x rate.
Worked example
Wall 10 m x 3 m = 30 sq m, less a door 1.0 m x 2.1 m = 2.1 sq m (above 0.5, so deducted) = 27.9 sq m. Putty at 1.5 kg per sq m = 42 kg, so three 20 kg bags allowing waste. Primer at 10 sq m per litre = 2.8 L, buy 3 L. Emulsion two coats at 8 sq m per litre: 27.9 x 2 / 8 = 7.0 L. Material cost at Rs 600 per bag, Rs 250 per litre primer, Rs 300 per litre emulsion = 1800 + 750 + 2100 = Rs 4650; labour 27.9 x Rs 35 = Rs 977; total Rs 5627 before overheads, profit and GST.
Traps
Forgetting the ceiling; deducting openings smaller than 0.5 sq m; using theoretical coverage on porous new plaster that drinks the first coat; quoting per litre when the client compares per sq m; omitting scaffold and masking from the rate.