Masonry Paint Calculator — Exterior Wall Paint Quantities

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.