Exterior Paint Calculator — House Walls and Cladding
Exterior paint projects need accurate estimates — running out and stopping part-way through a wall creates visible lap marks and colour mismatches. Enter your house perimeter and wall height to get a precise litre count.
How we calculate
Wall area = perimeter × height. Deduct 1.9 m² per door, 1.2 m² per window. Paint = (paintable area ÷ coverage) × coats × (1 + waste %). Cans = ⌈litres ÷ can size⌉.
Worked example
House with 30 m perimeter, 2.8 m walls, 2 doors, 6 windows, 2 coats, 10 m²/L, 15% waste. Wall area = 84 m², paintable ≈ 73.7 m². Paint ≈ 17 L → 4 × 5 L cans.
Common mistakes
- Using interior paint outside — it lacks UV and weather resistance.
- Underestimating rough or textured masonry which absorbs 20–30% more paint.
- Skipping primer on bare render or over a chalky surface.
- Painting in direct sunlight — paint dries too fast and leaves streaks.
Frequently asked questions
How much exterior paint does a house need?+
A typical semi-detached house with a 30 m perimeter and 2.8 m walls needs around 15–20 litres for two coats on smooth render, or 20–25 litres on rough textured masonry. Always buy from the same batch to avoid colour variation between tins.
Does exterior masonry need primer?+
Yes, new render, bare brick, or chalky old surfaces all need a masonry primer or stabilising solution before topcoat. Skipping primer causes the topcoat to absorb unevenly, reducing coverage and longevity.
Why does rough masonry need more paint than smooth walls?+
Textured surfaces have a larger effective area than they appear — the peaks and valleys in rough render can increase paint consumption by 20–30% compared to a smooth surface of the same measured dimensions. Use the higher end of coverage estimates or increase your waste allowance.
What is the best time of year to paint exterior walls?+
Spring and autumn are ideal — temperatures between 10 °C and 25 °C allow paint to cure properly. Avoid painting in frost, heavy rain, or direct midday sun, which causes the surface to dry too quickly and can trap moisture or leave lap marks.