MovePik

Exterior paint calculator for the walls of a house

Measure the walls to the eaves, add the gables as triangles, and get the gallons or liters, the cans or buckets to buy and the leftover.

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Measure the outside walls of each house or wing once. The paint is planned from these measurements.

Units

Changing a unit only changes how values are shown. Your measurements stay exactly as entered.

Feet and inches: type 12' 6", 12 6 (= 12 ft 6 in) or 12.5 (decimal feet). Inches alone: 30".

Houses and wings

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What this planner works out

Enter the outside walls up to the eaves, the gable triangles and the windows and doors you will not paint. With the coverage and can size from the label of your paint, the planner works out the paint for each coat, adds your allowance, and rounds up to whole cans or buckets. It shows the exact amount, the amount with allowance, what to buy, the leftover and the cost, and it can compare gallon cans with 5-gallon buckets of the same paint.

How to measure a house

  1. The footprint. Measure the length and width of the house along the walls you paint. An L-shaped house can be entered as an L, or split into wings, one entry per wing. If a wall is set back or sticks out, the rectangles option takes the measured perimeter.
  2. The wall height to the eaves. Measure from the bottom of the siding up to where the wall meets the roof. On ground that slopes, use an average height or split the walls into entries.
  3. Gables. Each end of a pitched roof has a triangle of wall above the eaves. Add it as a triangle under Painted areas: base width and height from the eaves to the top, the same rule as for an indoor gable in how to measure a room. Dormer cheeks, a chimney or a garage wall are rectangles or more triangles.
  4. Openings. Enter every window and door you will not paint with its width and height; the planner takes them off the walls. A window in a gable is entered as an opening of the walls too, because painted areas never subtract openings.

The method in plain words

  1. Walls: perimeter × height to the eaves, minus the openings.
  2. Gables: ½ × base × height for each triangle, times how many there are.
  3. Paint: area × coats ÷ coverage per coat, for each surface. The walls and the gables of the same paint are added up before rounding, so you never round up twice.
  4. Allowance: your percentage on top for rollers, sprayer losses and touch-ups.
  5. Cans: divide by the can size and round up, never down. What remains in the last can is the leftover; how pack rounding works shows why the allowance is added before rounding up.

Worked example in feet and gallons

A house 40 × 30 ft with 10 ft walls to the eaves, eight 3 × 5 ft windows, two 3 × 7 ft doors and two gables 30 ft wide and 8 ft high. The coverage of 350 sq ft per gallon is an example; use the figure on your own can. Two coats, 10% allowance:

  • Walls: 2 × (40 + 30) = 140 ft × 10 ft = 1,400 sq ft
  • Openings: 8 × 15 + 2 × 21 = 162 sq ft, so the walls are 1,238 sq ft
  • Gables: 2 × ½ × 30 × 8 = 240 sq ft
  • Total: 1,478 sq ft
  • Paint: 1,478 × 2 ÷ 350 = 8.446 gal, with 10% = 9.290 gal
  • 10 one-gallon cans or 2 five-gallon buckets, about 0.71 gal left over either way

Worked example in meters and liters

A house 12 × 8 m, 5 m to the eaves, ten 1.2 × 1.2 m windows, two 0.9 × 2.1 m doors and two gables 8 m wide and 3 m high. Example coverage 8 m² per liter per coat, two coats, 10% allowance, 10 L pails:

  • Walls: 2 × (12 + 8) = 40 m × 5 m = 200 m²
  • Openings: 14.4 + 3.78 = 18.18 m², so the walls are 181.82 m²
  • Gables: 2 × ½ × 8 × 3 = 24 m², total 205.82 m²
  • Paint: 205.82 × 2 ÷ 8 = 51.455 L, with 10% = 56.6 L
  • 56.6 ÷ 10 = 5.66, rounded up to 6 pails (60 L), about 3.4 L left over

A quick check of one triangle: two gables 7.2 m wide and 2.5 m high are 2 × ½ × 7.2 × 2.5 = 18 m². Leave the base empty and the planner asks for it instead of counting the gables as nothing.

Coverage on rough siding

The label states how far the paint goes in one coat on a given surface. Rough or porous surfaces soak up and hold more paint, so the same can covers less of them. Use the label’s figure for your surface, and if the label gives a range, the lower end is the cautious choice. If it gives one figure for the first coat and another for later coats, enter the lower, first-coat figure: the planner uses one coverage for every coat of paint, as paint coverage and coats explains. Painting one measured wall first and checking how far the first can went is a good check before you buy the rest.

Common mistakes

  • Measuring the gable from the ground. The gable height runs from the eaves line to the top, not from the ground. In the feet example, 18 ft from the ground instead of 8 ft from the eaves makes the two gables 540 sq ft instead of 240: 11.18 gal with the allowance, so 12 cans instead of 10.
  • Leaving out the gables. Walls measured to the eaves stop where the gables begin. Without the gables the same house comes to 1,238 sq ft and 7.78 gal with the allowance, so 8 cans: 2 short of the 10 it needs.

Limits and safety

  • Working at height: use a ladder or access tower as its maker says, and keep away from overhead power lines. In the US, see OSHA; in Great Britain, see the HSE. In other countries, check your national guidance.
  • Old paint: in the United States, homes built before 1978 may have lead-based paint, and scraping or sanding it releases lead dust. Read the EPA’s lead-safe renovation guidance for do-it-yourselfers before you prepare the surface.
  • Not covered: repairs, priming advice, weather or drying conditions, scaffolding, and anything structural.

For the deck, porch steps and fences, the deck, fence and patio stain calculator works out the stain, and the paint calculator plans the rooms inside.

Frequently asked questions

How do I measure a gable?

A gable is the triangle of wall between the eaves and the ridge on the end of a pitched roof. Measure its width at the bottom (the base, usually the width of that end of the house) and its height from the eaves line up to the top. Add it as a triangle under Painted areas: the planner takes half of base × height. Two identical gables are one row with How many 2.

What coverage should I use for rough siding?

The figure on the label of the paint you will use, for your kind of surface. Rough, porous or textured siding such as stucco, shingles or bare wood takes more paint than smooth siding, so it gets fewer square feet per gallon. Some labels give two figures; use the one for your surface, or the lower one if you are unsure. The planner has no coverage figure of its own and adds no extra for texture.

Should I buy gallons or 5-gallon buckets?

Enter the gallon can as the main size, then open Compare other can sizes of this paint on the paint card and add the bucket with its fill and price. The planner shows the lowest total among the sizes and prices you entered. In the example below, 10 gallons and 2 buckets hold the same amount, so only the prices decide.

Does it include trim, doors and the garage door?

Only what you add. Trim, fascia and window frames are usually a different paint: add it as its own material and its pieces as painted areas (a rectangle of length × face width). A door or garage door you paint in the wall color can stay in the wall area; one you paint differently is entered as an opening and, if you paint it, as its own painted area.

Can I plan the inside of the house too?

Yes, in the same project. Untick Outside walls of a house on a room and it becomes an ordinary room with a ceiling. The paint calculator starts with an indoor example instead.

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