Exterior Paint Calculator
Outside surfaces drink paint at very different rates: smooth render takes half as much as pebbledash, and a rough-sawn fence takes twice what planed timber does. Enter the house size or the area, pick the surface, and this calculator returns the litres, the tin combination and how much of it each coat uses.
Your measurements
Check your order
Your painting order
- Record the coating, colour, finish, coverage per coat and number of coats.
- Round the calculated litres or gallons to the actual tins or cans. Estimate primer separately.
- Check roller fabric and nap against the coating and surface; reuse suitable tools you already own.
Tools for this job
Choose applicators for the actual exterior coating and wall texture. Rough masonry may need a longer-nap roller than the one in a general painting kit.
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- Cover the open wall areas
Roller kit
Wooster Painter's Choice roller kit
A roller kit to consider for painting wall areas. Match the cover and nap to your paint and surface texture before choosing a kit.
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Angled brush
Wooster Shortcut 2-inch angled brush
An angled brush for the edges and trim a roller cannot reach. Check brush compatibility with the coating you plan to use.
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Already have suitable tools? Reuse them. These are optional product suggestions, not a complete equipment list or a hands-on comparison. Amazon may redirect Amazon.com links to local products or search results. Amazon.nl links search for alternatives, which may differ in brand, size and specification. Check suitability, seller, delivery and any import costs on your chosen store before ordering.
How much exterior paint do I need?
Exterior paint is worked out the same way as interior paint: the area to cover, times the number of coats, divided by the spreading rate, plus an allowance. The difference is that the spreading rate outside varies far more. A litre of masonry paint that covers 7 m² of smooth render will cover barely 3 m² of pebbledash, because the texture roughly doubles the true surface area and the paint has to fill every hollow.
That is why this calculator asks for the surface first. It sets a typical rate for smooth or rough masonry, rough-sawn or planed timber and decking, and lets you overwrite it with the figure printed on your own tin. The house-walls mode builds the area from the perimeter and eaves height, adds any gable ends, and deducts the doors and windows.
The formula
Wall area = Perimeter × Height to eaves + Gables × ½ × Gable width × Gable rise. Each opening is deducted at 1.7 m², which is the average of a standard door and a standard window with its frame.
Spreading rates by surface
These ranges explain the surface presets and are not verified specifications for every paint. Enter the actual rate on your tin, and check with a test patch when the surface is unusually porous or textured.
| Surface | Metric (m²/L) | Imperial (sq ft/US gal) | Coats |
|---|---|---|---|
| Smooth render, previously painted masonry | 6 to 8 | 245 to 325 | 2 |
| Rough render, Tyrolean, pebbledash | 2 to 4 | 80 to 165 | 2 |
| Bare brick or blockwork | 3 to 5 | 120 to 205 | Check product system |
| Rough-sawn fence panels and sheds (treatment) | 4 to 6 | 165 to 245 | 2 |
| Planed timber, cladding, windows (paint) | 10 to 12 | 410 to 490 | 2 plus primer on bare wood |
| Decking oil or stain | 8 to 12 | 325 to 490 | 2, the second thinner than the first |
Worked example
A detached two-storey house 8 m × 7 m has 30 m of wall all the way round and a hipped roof, so no gables. At 5 m to the eaves the gross wall area is 30 × 5 = 150 m². Deduct 8 doors and windows at 1.7 m² each = 13.6 m², leaving 136.4 m² to paint.
Smooth render at 7 m²/L needs 136.4 ÷ 7 = 19.5 litres per coat. Two coats = 39.0 litres. Add the 10% allowance and the answer is 42.9 litres. The metric tin solver offers four 10 L tins and three 1 L tins, totalling 43 litres. That is about 0.1 L above the allowance-inclusive order, or 4.0 L above the estimated paint actually applied. The result calls the latter left over; it includes the allowance.
Switch the surface to pebbledash at 3 m²/L and the same house needs 100 litres. Nothing else changes: this is the single biggest decision in the whole calculation, and the reason to check the texture before you buy.
How to measure a house from the outside
- Walk the perimeter with a long tape or a wheel, measuring each wall at ground level. Include the returns on a bay or a porch if you are painting them.
- Measure the height from the ground to the gutter at one point. On sloping ground use the tallest side.
- Count the gable ends (the triangular bits of wall under a pitched roof) and measure their width and the rise from eaves to ridge. Each one is half a rectangle.
- Wall mode deducts a rough 1.7 m² per opening. For large glazing or irregular doors, measure each opening, subtract it from the wall area and use the net-area mode. Add any reveals you will paint.
- For a fence, measure the run length and multiply by the panel height, then double it if you are treating both sides.
What else the job needs
- Preparation and primer: use the coating instructions to decide whether the surface needs cleaning, stabilising or a primer. The primer calculator gives a separate quantity estimate.
- Filler and repairs before you start. Cracked render is repaired with the render calculator, and paint will not bridge a crack for long.
- Surface treatment for algae or mould where required: follow the chosen cleaner instructions, including any rinse and drying time.
- Fence and decking: see the fence calculator for panel counts and the decking calculator for boards, then bring the area back here for the treatment.
- Masking and sheeting for windows, paths and plants. Masonry paint splashes are permanent on glass and block paving.
Fences, sheds and decking
A fence 20 m long and 1.8 m high has 36 m² per side. Both sides total 72 m². At the illustrative 5 m²/L rate, two coats need 72 × 2 ÷ 5 = 28.8 L before allowance, or 31.68 L with 10%. Leaving out a side or a coat halves the estimate incorrectly.
Decking oils and stains differ in coat count and coverage. Grooves and weathered timber can increase consumption, but there is no fixed extra percentage for every board profile. Use the product guidance or measure consumption over a test area.
Sources and assumptions
The model calculates rectangular elevations and triangular gables, deducts estimated openings, then divides the area for all coats by the chosen spreading rate.
- Dulux Trade Weathershield Smooth Masonry Paint: This named product quotes up to 16 m²/L. It demonstrates that the calculator’s broad surface estimates do not represent all masonry paints.
Before using this estimate
- Openings are estimated at 1.7 m² each. Use measured net area where large glazing or irregular elevations dominate.
- Use the label or a test patch for coverage, coats and preparation. The estimate does not include access equipment, repairs, separate primer or the extra surface area of detailed timber profiles.
Source notes reviewed . See how we check calculations and handle corrections.
Planning your order
Check the inputs before buying: measure the surfaces you need, then apply an allowance and round to whole packs. The guides include worked examples you can follow alongside this calculator.
Published by OrderEnough. This is a planning estimate: check the product specification and the assumptions above before ordering. Last updated . Read how we source our figures on the methodology page.