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Masonry Paint Calculator — Exterior Wall Paint Quantities
Calculate masonry paint for outside walls. Accounts for surface texture, pebbledash, render and brick with UK coverage rates.
Full height of exterior wall
Length of each wall section
Number of wall sections of this size
Each door subtracts 1.8 m² (a standard 1981×838 mm leaf is 1.66 m²; the extra allows for frame and reveal)
Each window subtracts 1.2 m²
For powdery, chalky or friable surfaces — apply before painting
Adds 10% extra for uneven surfaces and application losses
10% standard — consider 15% for very rough surfaces
Enter your supplier price for a cost estimate
Area per door opening (default 1.8 m²; a standard 1981×838 mm leaf is 1.66 m²)
Area per window opening (default 1.2 m²)
Stabiliser spreading rate (default 4 m²/L — Dulux Trade Weathershield Stabilising Primer Datasheet 304, 10/25 issue, quotes up to 10 m²/L on sound surfaces, but far less on the powdery surfaces it is used for)
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How We Calculate This
Our masonry paint calculator works by calculating the total exterior wall area, subtracting doors and windows, then dividing by the coverage rate for your surface texture. Exterior surfaces vary enormously in their paint absorption — rough pebbledash uses twice as much paint per m² as smooth render.
The formula
Litres needed = (Net wall area × Number of coats) ÷ Coverage rate per litre × Wastage factor
Net wall area = (Wall height × Wall length × Number of walls) − (Doors × 1.8 m²) − (Windows × 1.2 m²)
For example, a front wall 8m × 6m with smooth render, minus 1 door and 3 windows: Gross area = 48 m². Net area = 48 - 1.8 - 3.6 = 42.6 m². For 2 coats at 10 m²/L: 42.6 × 2 ÷ 10 = 8.5 L, plus 10% wastage = 9.4 L. You'd need 1 × 10L tin or 2 × 5L tins.
Coverage rates by surface texture
- Smooth Render: 10 m²/L — standard rendered walls with a flat finish (a conservative practical two-coat rate matching Leyland Trade Truguard Smooth Masonry)
- Textured Render: 7 m²/L — roughcast or stippled render finishes (indicative estimate)
- Pebbledash: 5 m²/L — heavily textured surface absorbs the most paint
- Bare Brick: 6 m²/L — porous brick absorbs significantly (indicative estimate)
These are conservative, real-world two-coat rates. They sit deliberately below the headline lab figures some makers publish on ideal smooth surfaces — Dulux Trade Weathershield Smooth Masonry and Sandtex Ultra Smooth quote up to 14-16 m²/L on smooth low-porosity render, dropping to about 4-6 m²/L on textured surfaces such as pebbledash. Always check the datasheet for your specific product and do a test area, as coverage varies with surface roughness and porosity. Two coats are standard for exterior masonry to achieve full coverage and protection. If the surface is powdery, apply stabilising solution first (Dulux Trade Weathershield Stabilising Primer Datasheet 304, 10/25 issue: up to 10 m²/L on sound surfaces, but expect roughly 4 m²/L on the friable surfaces it is used for) and allow to dry before painting.
Frequently Asked Questions
A typical UK semi-detached house front is around 6m wide × 7m high (42 m²). After subtracting a door and 3 windows, that leaves roughly 36 m² of paintable area. For smooth render with 2 coats at a conservative practical rate of 10 m²/L (the real-world figure for two-coat coverage; manufacturers such as Dulux Weathershield Smooth and Sandtex Ultra Smooth quote higher headline rates of up to 14-16 m²/L on ideal smooth surfaces), you need about 7.2 litres — so a single 10L tin would cover it with some spare for touch-ups.
Pebbledash has a very rough, uneven surface that dramatically increases the actual surface area compared to its flat measurements. The stones create nooks and crevices that absorb paint. Pebbledash covers only about 5 m²/L compared to 10 m²/L for smooth render — essentially double the paint. Using a long-pile masonry roller helps get paint into the textured surface.
Stabilising solution is needed if your render or masonry is powdery, chalky or friable. Rub your hand across the surface — if white powder comes off, you need to stabilise before painting. Products like Dulux Trade Weathershield Stabilising Primer (Datasheet 304, 10/25 issue) or Sandtex Stabilising Solution seal the surface so the paint can adhere properly. The current datasheet quotes coverage up to 10 m²/L on sound surfaces, but on the powdery, absorbent surfaces it is actually used for you should expect far less — roughly 3-5 m²/L (the calculator defaults to 4 m²/L).
Dulux Weathershield and Sandtex 365 are among the most popular masonry paints in the UK, both offering long-term protection guarantees: Dulux Weathershield carries a 15-year guarantee, while Sandtex 365 All Weather claims up to 20 years' protection. For maximum durability, choose a product with high flexibility to cope with the UK's freeze-thaw cycles. Smooth masonry paint is easier to apply but textured paint (like Sandtex Fine Textured) hides minor surface imperfections. For interior walls, try our Paint Coverage Calculator. For wood features like fences and decks, see our Wood Stain Calculator.
The best time to paint exterior masonry in the UK is late spring to early autumn (May to September) when temperatures are consistently above 10 degrees C and rain is less frequent. Avoid painting in direct strong sunlight, rain, frost or high winds. The surface must be completely dry before application — allow 24 hours after rain before painting.
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Last updated: February 2026
Verified against UK standards · estimates only, confirm with your supplier.