Wall Area and Paint Calculator
Net wall area with openings deducted, plus paint and filler.
Inputs
Result
Formula
| Gross area | A = length × height |
| Openings | A = count × area each |
| Net area | A = gross − openings |
| Paint | V = net × coats ÷ coverage |
| Filler | W = net × 1.5 kg/m² |
| Buckets | N = ceil(paint ÷ 5) |
A 10 m wall at 3 m with two 1.8 m² openings, 10 m²/L coverage and two coats: 30.00 m² gross, 26.40 m² net after deducting 3.60 m², openings at 12%, 5.28 L of paint — two 5 L tubs.
FAQ
Why is coverage a range rather than a fixed number?
Spreading rate varies with substrate absorption, paint viscosity and application method. The same tub covers 12 m² on a fair plaster surface and 6 m² on bare cement render. Manufacturers quote theoretical figures from standard panels, so take 20-30% off in practice. Estimate on the pessimistic side and buy an extra tub — colour matching depends on the same batch.
Does filler need two coats?
Yes. The first fills and levels and is sanded when dry; the second closes the surface and is sanded to within 2 mm. A single coat leaves local hollows over 3 mm thick, which crack and shell off. Keep total filler thickness at 2-3 mm — beyond 5 mm it debonds, because filler is weaker than the render beneath.
How does new work differ from repainting?
New render needs a bonding agent to bind dust and improve adhesion before filling. Repainting requires removing every hollow and flaking patch first, or the new coat leaves with the old. Where the previous finish was oil-based, abrade it or use a bridging primer — water-based paint straight on top will lift and wrinkle.
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Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.