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AnswerOpenings come out before coatsExterior paint quote calculatorInterior paint is a different pageWorked example — 40 ft × 9 ft, two doors, six windows, 2 coats, 350 ft²/gal, 10% waste
Gross wall is 40 × 9 = 360 ft². Two 21 ft² doors and six 15 ft² windows leave 228 ft² paintable. Two coats plus 10% waste is 228 × 2 × 1.10 = 501.6 ft² of film. At the calculator default of 350 ft² per gallon, 501.6 ÷ 350 = 1.433…, which purchases as 2 US gallons. A third accent colour is another line.
Painting calculator
Exterior paint calculator
Exterior-paint gallons from wall length, height, openings, coats and labelled coverage. Interior rooms use the paint calculator.
By Feroz Sheikh · Formula PAINT-EXT-001 v1.0.0 · Tested formula
PAINT-EXT-001v1.0.0Project inputs
Enter your measurements. Switching units converts the same project, including coverage and unit rates. Package yields keep the unit printed beside each field.
Calculated result
Exterior paint gallons
PAINT-EXT-001(wall length × height − openings) × coats × (1 + waste) ÷ coverage
Gross wall area
Paintable area
Area across coats + waste
Planning estimate, not engineering advice. Confirm site measurements and product specifications. Calculation limits.
Exterior wall length times height, minus door and window openings, times coats, divided by labelled exterior coverage after waste.
- Measure each elevation. Measure gables separately as base × vertical height ÷ 2. On a separate takeoff, enter half the base as wall length, the gable height and measured openings; keep waste separate.
- Exterior coverage is not interior coverage. Use the can you will roll outside.
- Trim paint is the trim calculator.
Add your project costs
Enter supplier prices and any labour, equipment or delivery costs. Pick a currency — badges, inputs, and totals follow.
Costs use the can rate you type. Construclytic does not fetch paint prices. Primer, ceiling gallons and cut-and-roll labour stay on their own lines. For GCC projects, select QAR, AED, SAR, KWD, OMR or BHD and enter local supplier rates.
Openings come out before coats
Measure total wall length and height to the eave. Deduct doors and windows you will not paint — planning defaults are 21 ft² per door and 15 ft² per window, both editable. Two coats double the film; you still round purchase up to a whole gallon.
Stucco, brick and rough cedar need a lower coverage figure than a smooth clapboard. Enter the number from the selected exterior product. Example gallons for 1,000 to 3,000 sq ft houses, on one storey and two, are in exterior paint gallons by house size. Those rows fix the rectangle, the eave height and the openings. A measured perimeter still belongs in the calculator on this page. Interior rooms in litres, not gallons, are in how many litres of paint per m².
Exterior paint quote calculator
Coverage is a labelled assumption, not a price. Behr Premium Plus Exterior Flat No. 4050 lists 250–400 sq ft per US gallon, and Sherwin-Williams Duration Exterior Acrylic Flat K32 lists 250–300 sq ft per US gallon. Those ranges are the ones already recorded on exterior paint gallons by house size: the Behr sheet is marked 10/25 and the Duration sheet is marked 3/2026, both opened 27 October 2026. The 350 ft² per gallon figure in the worked example is only the exterior paint calculator’s planning default. Replace it with the can you will buy.
The film on that 40 × 9 ft wall is 228 × 2 × 1.10 = 501.6 ft². Gallons to buy = ceil(501.6 ÷ coverage). At 350 ft² per gallon that is 1.433…, which rounds up to 2 US gallons. At 250 sq ft per gallon it is 2.0064, which rounds up to 3 US gallons. At 300 and at 400 sq ft per gallon the purchase stays 2 US gallons.
Material line = whole gallons × the price per gallon you enter. After the exterior paint calculator rounds the quantity, open the Paint cost calculator and enter the current local rate for the exact exterior product. Leave the extra allowance at 0, because the 10% waste is already in the gallon count. Two gallons is then 2 × that rate, and the 250 sq ft per gallon case is 3 × the same rate. The calculator multiplies the purchase quantity by that dated rate; it does not substitute a web-average or live store price. The sample rate already in the tool is not an exterior-paint market price. Hand the whole-gallon quantity to a material-cost line. That result is paint material only, not an installed quote. Keep labour, surface preparation, primer, access equipment, tools, tax and delivery as separate lines.
| Coverage assumption | 501.6 ÷ coverage | US gallons | Material line |
|---|---|---|---|
| 350 ft²/gal (calculator default) | 1.433… | 2 | 2 × your price/gal |
| 250 sq ft/gal (Behr No. 4050 and Duration K32 low end) | 2.0064 | 3 | 3 × your price/gal |
| 300 sq ft/gal (Duration K32 high end) | 1.672 | 2 | 2 × your price/gal |
| 400 sq ft/gal (Behr No. 4050 high end) | 1.254 | 2 | 2 × your price/gal |
Interior paint is a different page
Rooms, ceilings and trim enamel are not this takeoff. Primer is its own product. Measure each gable as base × vertical height ÷ 2, separately from the wall below the eave. On a separate exterior-paint takeoff, enter half the base as wall length and the gable's vertical height; deduct only measured openings in that triangle. Keep waste separate. For the same product and colour, combine the areas across coats and waste before dividing by labelled coverage and rounding to whole gallons; adding separately rounded gallons can overbuy.
Do it in order
- Enter wall length and eave height, then door and window counts.
- Type coats and the coverage from the selected exterior can. 350 ft² per gallon is only the calculator default.
- Round up to whole gallons, enter that count and the current local rate in the paint cost calculator with the extra allowance at 0, then keep labour, prep, tax and delivery as separate estimate lines.
Planning boundary
This estimates gallons and can hand the whole-gallon quantity to a material-cost line. It does not specify prep, moisture, lead-safe work, a live paint price or an installed quote.
Sources checked
Each link supports the point named in the text. A citation is not a product endorsement or a price for your site.
- Sherwin-Williams Paint FAQ — typical coverage varies by surface and desired coverage
- BEHR — How Much Exterior Paint to Buy
- Benjamin Moore — Estimating Paint Jobs
- Behr Premium Plus Exterior Flat No. 4050 technical data sheet — 250–400 sq ft per gallon (sheet marked 10/25, opened 27 October 2026, as recorded on the gallons-by-house-size guide)
- Sherwin-Williams Duration Exterior Acrylic Flat K32 — 250–300 sq ft per gallon (data sheet marked 3/2026, opened 27 October 2026, as recorded on the gallons-by-house-size guide)
How does the exterior paint quote calculator work?
A 40 × 9 ft exterior wall needs 2 US gallons after two coats, 10% waste and the calculator default of 350 ft² per gallon. Gallons = ceil((wall length × height − openings) × coats × (1 + waste) ÷ coverage). The material line is those whole gallons times the price per gallon you enter in the paint cost calculator. It is not an installed quote.
Do gables use the same height?
No. Measure the gable's vertical height above the eave. Its area is base × vertical height ÷ 2; use half the base as wall length in a separate takeoff. Do not guess missing gable area by raising waste.
Is this the interior paint tool?
No. Interior rooms open the paint calculator.
Does coverage include primer?
No. Primer is a different product and a different calculator.
Is the Paint cost result an installed quote?
No. It is the whole-gallon quantity multiplied by the dated local material rate you enter. Labour, prep, tools, access, tax and delivery stay separate.