Exterior Paint Calculator — Masonry, Timber & Render
Calculate how much exterior paint, primer and undercoat you need for house facades, rendered walls and timber cladding. Accounts for the lower coverage rate of masonry paint on absorbent surfaces and the extra coats needed for previously unpainted or weathered surfaces.
How the exterior paint calculator works
- 1Facade area = perimeter × height, minus windows and doors
- 2Masonry/render coverage: 5–8 m²/L (first coat on bare render), 8–10 m²/L (recoating)
- 3Timber cladding: 8–12 m²/L for opaque paint, 6–10 m²/L for stain/preservative
- 4Primer or stabilising solution required on bare or flaky surfaces before top coat
- 5Two top coats minimum on any exterior surface for durability
- 6Round up to nearest 5 L or 10 L tin
Worked example
Semi-detached house, rendered facade: 80 m² net area. First-time painting. Two top coats of masonry paint at 7 m²/L.
Stabilising primer: 80 ÷ 6 = 14 L. First coat: 80 ÷ 7 = 11.5 L. Second coat: 80 ÷ 7 = 11.5 L. Total: 14 L primer + 23 L masonry paint → 1× 10 L primer + 3× 10 L masonry paint.
Frequently asked questions
How long does exterior paint last?
High-quality masonry paint on render typically lasts 10–15 years before repainting. Timber cladding paint or stain needs recoating every 3–7 years depending on aspect (south-facing weathers faster) and product quality.
What exterior paint coverage rate should I use?
Smooth render: 8–10 m²/L. Rough textured render (pebbledash): 4–6 m²/L (much higher absorption). Smooth timber: 10–12 m²/L. Weathered or chalky surfaces: use a stabilising primer first and calculate at 5–6 m²/L for the first coat.
Do I need primer for exterior walls?
Yes — bare render and new masonry must be primed with a stabilising primer or diluted first coat (masonry paint thinned 10%). Weathered or chalky surfaces also need stabilising before top coats. Skipping primer leads to poor adhesion and early failure.
Can I paint exterior walls in winter?
Avoid painting when the temperature is below 5°C or above 35°C, in rain, or when frost is forecast within 24 hours. The ideal temperature range is 10–25°C with low humidity. Masonry must be dry — allow 48 hours after rain.
What is the difference between masonry paint and render paint?
Modern flexible masonry paint is designed for both brick, block and rendered surfaces. Specialist render paint (silicone or mineral) is more breathable and crack-bridging. For smooth modern render, silicone paint offers the best long-term performance.