Calculate wall surface area for painting, plastering, rendering, and tiling. Enter wall dimensions and openings to get net area instantly.
Calculate floor, wall, and sloped surface areas from dimensions
Measure wall width and height in metres. Multiply to get gross area, then subtract doors (typically 1.9 m² each) and windows (typically 1.5 m² each). One litre of paint covers approximately 10 m² per coat on smooth walls.
Undercoat plaster: 2mm thickness requires about 2kg/m². Skim coat: 2mm requires about 2kg/m². A 25kg bag of multi-finish covers about 10 m² at 3mm thickness. Order 10% extra for waste.
Scratch coat (10mm): about 18kg/m² of render. Top coat (6mm): about 11kg/m². A 25kg bag of render covers about 1.5 m² at 10mm. Add 10-15% waste for uneven walls.
Calculate net wall area, then divide by tile size (including grout gap). For 300×600mm tiles: 1/(0.3×0.6) = 5.56 tiles/m². Add 10% waste for straight lay, 15% for diagonal. Order extra — dye-lots change between batches.
A = width × height
A_net = A - (doors × door_area) - (windows × window_area)
litres = A_net / coverage_per_litre × coats
tiles = ceil(A_net × (1 + waste%) / tile_area)
For rendering over 15mm thick, external wall insulation systems, or damp-proofing, consult a specialist contractor. Structural wall modifications (removing walls, enlarging openings) require a structural engineer and building control approval.
Gross area = 10 m². Minus door (1.9 m²) = 8.1 m². At 10 m²/L per coat, 2 coats: 8.1 × 2 / 10 = 1.62 litres. Buy a 2L tin.
Net wall area × thickness in mm × 1.8 kg = kg of render needed. For 20 m² at 10mm: 20 × 10 × 1.8 = 360 kg = 15 bags of 25kg. Add 10% waste: 17 bags.
For 300×600mm tiles: 1/(0.3×0.6) = 5.56 tiles/m². For 600×600mm: 1/(0.6×0.6) = 2.78 tiles/m². For 150×150mm: 1/(0.15×0.15) = 44.4 tiles/m². Add 10% waste.
Skirting boards are typically 100-150mm tall. For a 4m wide wall, that's 0.4-0.6 m² — usually negligible for paint calculations but worth subtracting for expensive tiles.