Estimation, Measurement and Material Calculation
This domain tests measured take-off and quantity calculation: converting a room into square metres, deducting openings correctly, and converting area into litres, packs and labour days.
Measurement rules
Measure in metres to two decimals. Wall area = perimeter × height; perimeter = 2 × (length + breadth). Ceiling area = length × breadth. Deduct openings larger than about 0.5 m², and add for reveals, jambs and returns where the specification requires. Linear items - skirting, dado rail, border - are measured in running metres. Separate items for primer, putty, each finish coat and scaffolding.
Quantity formula
Litres per coat = area ÷ coverage (m² per litre). Total litres = litres per coat × number of coats. Add 5–10% wastage for texture, rough surfaces and touch-up. Labour is estimated from output per painter-day, typically 25–35 m² for emulsion on normal walls.
Worked example
Room 5.0 × 3.5 m, height 3.0 m, one door 0.9 × 2.1 m, two windows 1.2 × 1.2 m, two coats of emulsion at 10 m² per litre.
- Perimeter = 2 × (5.0 + 3.5) = 17.0 m; wall area = 17.0 × 3.0 = 51.0 m².
- Deductions = 1.89 + (2 × 1.44) = 4.77 m², so paintable area = 46.23 m².
- Two coats = 92.46 m²; ÷ 10 = 9.25 L; add 8% = 9.99 L, so buy a 10 L pack. The reasoning at each step matters more than the final figure.
Traps that cost marks
Deducting small openings and then running short; forgetting the ceiling or dado; quoting litres when the client asked for m²; leaving out scaffolding and masking.