Exterior Paint Calculator

Q: How much exterior paint do I need per square metre?

Exterior masonry paint typically covers 5-8 m2 per litre on a rough or textured surface such as roughcast or pebbledash, and 8-12 m2 per litre on smooth painted masonry. Exterior timber paint covers 10-14 m2 per litre. Always use the spreading rate printed on the tin for your specific product. Two coats are standard for all exterior surfaces - bare or unpainted masonry may require a masonry primer or stabilising solution first, which is applied at a similar spreading rate.

Q: What is the best exterior paint for masonry?

For brick, render, and block masonry, use a flexible masonry paint or smooth or textured masonry coating. Smooth masonry paint gives a clean finish and is easy to apply by roller. Textured or heavy-duty masonry coatings fill hairline cracks and offer better weatherproofing on older, porous walls. For walls affected by algae, moss, or organic growth, apply an exterior fungicidal wash before painting and use a paint with built-in fungicide. Microporous or breathable masonry paint allows moisture vapour to escape, reducing the risk of paint peeling on walls that are not fully dry.

Q: Can I paint exterior walls in wet or cold weather?

Most exterior paints should not be applied below 5 degrees C or above 30 degrees C, or when rain is expected within 4-6 hours of application. Cold temperatures slow drying and can prevent proper film formation. Rain before the paint has dried will wash it off or leave tide marks. Avoid painting in direct strong sunlight as this can cause the surface to dry too fast, leaving brush marks and reducing adhesion. Early morning and late afternoon in dry conditions with a light breeze are ideal painting conditions.

Q: How do I prepare exterior walls before painting?

Good preparation is essential for exterior paint to last. Clean the surface with a pressure washer or stiff brush to remove dirt, algae, moss, and loose material. Allow to dry fully - masonry can hold moisture for weeks after rain. Remove loose or flaking paint by scraping. Fill cracks and holes with exterior filler or mortar. Apply a masonry stabilising solution to areas of friable or powdery render. Prime bare timber with a wood primer. Apply two coats of exterior paint, allowing full drying time between coats (typically 4-6 hours in good conditions, or as specified on the tin).

Q: How long does exterior paint last?

Good quality exterior masonry paint applied to a properly prepared surface should last 5-10 years before needing repainting. Budget products or poorly prepared surfaces may need repainting every 3-5 years. Timber surfaces are more demanding - exterior timber paint or stain typically lasts 3-7 years depending on exposure and wood quality. South-facing and exposed walls fade and weather faster than sheltered, north-facing walls. Regular light maintenance (cleaning, spot filling, and touch-ups) significantly extends the life of any exterior paint system.

Q: How much exterior paint do I need for a typical house?

A typical 3-bedroom semi-detached house with approximately 80-100 m2 of masonry wall area (deducting windows and doors) needs approximately 10-20 litres of masonry paint per coat on smooth surfaces, or 15-30 litres on rough textured surfaces. Two coats are always recommended. Large purchases are more economical in 10 or 15 litre trade tins. Use the calculator above to enter your actual wall dimensions for a precise quantity.

Masonry paint, primer, and woodwork paint by elevation - with opening deductions and best-fit tin sizes

Masonry / Wall Paint

Paint Type

Topcoat Coats

Coverage (m²/L) Smooth: ~5-7 m²/L ◆ Textured: ~3-4 m²/L ◆ Limewash: ~4-6 m²/L

Include stabilising primer coat Apply to friable, powdery, or previously unpainted render / masonry

Stabiliser Coverage (m²/L)

Exterior Woodwork Paint (fascias, soffits, window frames, doors)

Woodwork Finish

Topcoat Coats

Coverage (m²/L) Gloss / satin: ~13-16 m²/L ◆ Microporous: ~12-15 m²/L

Include exterior wood primer / undercoat

Primer Coverage (m²/L)

Preferred Tin Sizes

Tick the sizes available in your chosen paint. The calculator picks the best combination to minimise waste.

Waste Allowance (%)

10%

10% is typical. Increase for complex gable ends, irregular elevations, or pebbledash surfaces.

Elevations

Global Woodwork Totals (across all elevations)

Enter total m² of exterior woodwork - fascias, soffits, window frames, doors, gates, etc. Use the guide in the sidebar.

Fascia & Soffit (m²) Fascia boards + soffits combined

Window Frames (m²) ~0.5-1.0 m² per window

Doors & Frames (m²) ~1.8 m² per door face (painted both sides = 3.6 m²)

Other Woodwork (m²) Gates, bargeboards, decorative timber, etc.

Job Costing (optional)

Masonry paint per litre

Stabiliser per litre

Woodwork paint per litre

Wood primer per litre

Labour cost

Rate x total area

UK Market PricesFills in the material cost fields with current UK market prices. You can review and edit each price before applying.

Results

Net Masonry Area
-
m² (less openings)

Total Woodwork

m²

Total Paint to Buy

litres (all paints)

Paint Breakdown

Surface / Paint	Area	Coats	Litres Needed	Litres to Buy	Best Tin Combo

Elevation Breakdown

Elevation	Gross Area	Openings	Net Masonry Area

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Frequently Asked Questions

How much exterior paint do I need per square metre?

Exterior masonry paint: 5-8 m²/litre on rough/textured surfaces; 8-12 m²/litre on smooth painted masonry. Exterior timber paint: 10-14 m²/litre. Two coats are standard. Always check the spreading rate on your specific tin - products vary significantly.

What is the best exterior paint for masonry?

For brick, render, and block: flexible masonry paint (smooth for clean finish, textured for filling hairline cracks). On walls with algae or moss: apply fungicidal wash first and use paint with built-in fungicide. On damp or non-fully-dry walls: use microporous/breathable masonry paint to prevent peeling.

Can I paint exterior walls in wet or cold weather?

Do not apply below 5°C or above 30°C, or when rain is expected within 4-6 hours. Avoid direct strong sunlight - it dries the surface too fast, leaving brush marks. Best conditions: early morning or late afternoon in dry weather with a light breeze.

How do I prepare exterior walls before painting?

1. Pressure wash to remove dirt, algae and loose material. 2. Allow to dry fully (masonry holds moisture for weeks). 3. Scrape loose or flaking paint. 4. Fill cracks with exterior filler or mortar. 5. Apply stabilising solution to powdery render. 6. Prime bare timber. Then two coats of exterior paint with full drying time between.

How long does exterior paint last?

Good quality masonry paint on a properly prepared surface: 5-10 years. Budget products or poor preparation: 3-5 years. Exterior timber paint or stain: 3-7 years. South-facing walls weather faster. Regular cleaning and touch-ups significantly extend any paint system's life.

How much exterior paint do I need for a typical house?

A typical 3-bed semi with ~80-100 m² of wall area needs approximately 10-20 litres per coat (smooth) or 15-30 litres per coat (rough/textured). Two coats recommended. Large quantities are more economical in 10 or 15 litre trade tins. Enter your actual dimensions above for a precise figure.

Measuring Elevations

Measure each elevation (front, rear, each side) separately as width x height
Height = from DPC / ground level to the top of the wall or soffit line
Deduct all windows and doors that will not be painted with masonry paint
Gable ends: measure the rectangular portion then add the triangular area - or add 10-15% to the wall area
Pebbledash and rough textured surfaces absorb more paint; use 3-4 m²/L rather than 5-7 m²/L

Typical Coverage Rates

Paint type	m²/L
Smooth masonry paint	5-7
Textured masonry	3-4
Sandtex / Weathershield	5-6
Pebbledash surface	2-3
Limewash	4-6
Stabilising primer	5-8
Exterior gloss / satin	13-16
Microporous exterior	12-15
Exterior wood primer	11-13

Woodwork Area Guide

Item	Approx m²
Front door (both faces)	3.6
Casement window (small)	0.5
Casement window (large)	1.0
Fascia board (per LM)	0.15
Soffit board (per LM)	0.15-0.3
Barge board (per LM)	0.15
Garage door	7-9

Preparation Tips

Apply stabilising primer to any friable, powdery, or chalky render before painting
Fill all cracks with exterior filler or flexible sealant before priming
Never paint in rain, frost, or temperatures below 5◆C
New render should be left to cure for at least 4-6 weeks before painting
Brush apply the first coat - do not roller on rough render as back-roller coverage is poor
A second coat applied within 24 hrs (wet-on-wet) gives better adhesion than waiting

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Exterior Paint Calculator

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