How Much Paint Do You Need for a House Exterior?

For a rectangular wall, multiply width by average paintable height. A 40 ft wall 10 ft to the eaves is 400 sq ft. Repeat for all sides rather than doubling one elevation; additions, porches, and attached garages make opposite walls surprisingly different.

Measure a triangular gable as half × base × vertical gable height. A 24 ft-wide gable rising 8 ft above the eaves adds 96 sq ft. Do not use the sloping roof-edge length in that formula. A trapezoid around a shed roof can be split into a rectangle and triangle.

Metric works the same way. A 12 m elevation averaging 3 m high is 36 m²; a 7 m gable with 2.4 m rise adds 8.4 m². Keep a sketch for north, south, east, and west elevations so a small return does not vanish from the order.

Subtract garage doors, broad window banks, and other large unpainted openings. A standard door and several average windows can be left in gross wall area on a rough estimate because brushing around them, overlap, and surface texture consume paint. For a precise takeoff, subtract their measured area and add trim separately.

Do not subtract openings that are being painted in the same colour unless their material uses a different coating. Louvered shutters and ornate doors can use more paint per apparent square foot than flat siding, so their face area is a poor predictor of labour and yield.

Brick, stone, roof surfaces, and large glass panels should come out of siding area when they remain unpainted. Masking them affects labour and sundries, not finish-paint volume. Note these surfaces on the sketch so the cost estimate still captures protection work.

Body colour usually covers the largest wall area. Fascias, soffits, corner boards, window casings, and railings form a second takeoff. Measure broad soffits by area and narrow trim by linear feet or metres, then use the product’s stated linear coverage where available.

Doors are commonly estimated individually after measuring both sides that will be painted. A paneled door has edges and recesses; allow more than its simple face area. Metal doors may need a different primer from weathered timber, while PVC or vinyl requires compatibility checks before coating.

Primer is not automatically one-for-one with finish paint. Spot-priming bare patches may use a fraction of a gallon; a full coat over chalky masonry or a major colour change may approach the whole wall area. Put primer on its own calculator line and select it for the substrate.

Suppose net siding area is 2,400 sq ft and the chosen paint is rated at 375 sq ft per US gallon. One coat requires 2,400/375 = 6.4 gallons. Two coats require 12.8 gallons, before allowance, so the practical order might be 14 gallons depending on container sizes and surface.

Metric example: 220 m² of wall with a stated spreading rate of 10 m² per litre needs 22 litres per coat. Two coats need 44 litres before allowance. If the label gives a range such as 8–12 m²/L, use the lower figure for a rough or porous surface until a test area proves otherwise.

The paint calculator handles arithmetic, but input the coverage of the exact product and application method. Do not combine US and imperial gallons: a US gallon is about 3.785 litres; an imperial gallon is about 4.546 litres. Modern UK retail paint is generally sold by litre.

Smooth, previously sealed siding tends to approach label coverage. Deep-textured stucco, split-face block, rough-sawn timber, and heavily weathered masonry expose more surface than their flat dimensions show. They also hold paint in recesses, reducing the area covered per litre or gallon.

Spraying is fast on broad elevations but creates overspray and leaves paint in hoses and equipment. Back-rolling may be required for adhesion or texture penetration and changes production, though not necessarily the specified dry-film build. Brush-and-roll work loses less to airborne spray but uses paint around joints and edges.

Test a known area when the substrate is questionable. If one gallon covers only 280 sq ft on the first coat, revise the remaining order before opening every container. The second coat may spread farther once suction is controlled, so track coats separately.

Add around 10 percent to a sound measured takeoff for normal exterior handling, texture variation, and touch-up. Intricate cladding or spraying in breezy conditions may need more. A huge “just in case” margin is not a substitute for measuring gables and coat count.

Where several cans form one colour, box them together in a clean larger container or mix between cans according to the manufacturer’s advice. Minor tint differences can show at the middle of a sunlit wall. Keep batch information and reserve a labeled amount for future repairs.

Container sizes influence rounding. A calculated 12.8 US gallons may be bought as two 5-gallon pails plus three or four singles, depending on allowance and return policy. In the UK, combinations of 10 L, 5 L, and smaller tins may minimize unused material without risking a mid-wall shortage.

Washing, scraping, sanding, repairs, caulking, and drying come before finish paint. Paint over loose coating only makes the loose layer heavier. Moisture sources, failed flashing, and rotten boards should be repaired rather than sealed behind an expensive colour.

Lead-safe rules can apply to older painted homes, and high elevations require proper access equipment. Skip DIY ladder work where safe three-point contact cannot be maintained or where overhead lines, steep ground, or brittle roofing complicate access. Quantity is the easy part of those jobs.

Use the paint cost calculator with separate quantities for body, trim, doors, and primer, then add masking, caulk, repairs, equipment, and labour. A premium product with higher reliable coverage may cost less per completed square foot than a cheap paint needing an additional coat.