Exterior Paint Calculator
Enter the size of the house, its gable ends and openings, the length and width of the trim, the coats and the area one gallon covers, and get the gallons of exterior paint and primer, rounded up once, with the working shown for an example.
Estimates for planning, not professional advice. Read the full notice.
Example: a house with its trim painted
7 gallons of exterior paint
- Area to paint, walls and trim 1,067 ft²
- Paint before rounding 6.1 gallons
- Primer 4 gallons of primer
Estimate for planning, from what you entered and the product data shown. Check product labels and your supplier before you buy.
Your project
Enter a size to see your total.
Each product is rounded up once for the whole project, so the total can be less than the items bought alone added together. A line counted from a cut layout (sheets, boards or tiles laid out piece by piece) is counted for each item and added.
Shopping list
| Item | Size | Buy |
|---|---|---|
| Exterior paint | gallons of exterior paint | 7 |
| Primer | gallons of primer | 4 |
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Worked example: a house with its trim painted
Show the working
- Gross wall: the distance round the house times the wall height 140 ft × 8 ft = 1,120 ft²
- Openings: every door and window at its own size 81 ft² = 81 ft²
- Net wall: gross wall less the openings 1,120 ft² − 81 ft² = 1,039 ft²
- Trim: its length times the width of its painted face 84 ft × 4 in = 28 ft²
- Area to paint: net wall plus trim 1,039 ft² + 28 ft² = 1,067 ft²
- Gallons: area times coats, divided by the area one gallon covers 1,067 ft² × 2 coats ÷ 350 ft² = 6.1 gallons
- Round up once, to whole gallons 6.1 gallons = 7 gallons of exterior paint
Assumptions
The figures behind the example. Sourced figures link to their source below; a default is a starting value to check against your label or supplier.
| Assumption | Value | Details and changes |
|---|---|---|
| Wall paint coverage | 350 ft²/gal[1] | |
| Default PaintCare's figure to use when the coverage rate is unknown. The maker ranges are facts bm-n550-coverage and sw-k36-coverage. | ||
| Primer coverage | 300 ft²/gal | |
| Default Not read from a maker's own sheet. Check your label or supplier. | ||
| Surface roughness factor | 1 times | |
| Default Our assumption; PaintCare says rough textures may need up to 50 percent more paint (fact paintcare-rough-more). Check your label or supplier. | ||
Feet and inches, like 12' 6"
Gallons of paint by coverage and coats
Gallons of paint for the example house and trim, by the area one gallon covers and the number of coats
| Coverage of one gallon | One coat | Two coats | Three coats |
|---|---|---|---|
| 250 sq ft | 5 gallons of paint | 9 gallons of paint | 13 gallons of paint |
| 300 sq ft | 4 gallons of paint | 8 gallons of paint | 11 gallons of paint |
| 350 sq ft | 4 gallons of paint | 7 gallons of paint | 10 gallons of paint |
| 400 sq ft | 3 gallons of paint | 6 gallons of paint | 9 gallons of paint |
| 450 sq ft | 3 gallons of paint | 5 gallons of paint | 8 gallons of paint |
Each cell is worked out on its own for the example walls and trim, rounded up once to whole gallons. The coverages are sizes entered for the table: use the figure printed on your own can.
Questions
How many gallons of paint does a house exterior take?
Add the net wall area, any gables and the trim area, multiply by the coats, divide by the area one gallon covers and round up once. The example shows each step, and the coverage table shows how the gallons move with the coverage and the coats.
Do I paint the trim?
Trim is a separate area here: enter its total length and the width of its painted face, and it is added to the walls. Leave the trim length at a small figure if you are not painting it, and add soffit or fascia area in its own field if you are.
Why does a rough surface need more paint?
PaintCare says rough textures may need up to fifty percent more paint. The texture factor multiplies the area; it starts at smooth and you can pick a medium or rough factor.
Sources (1)
-
Buy the Right Amount of Paint to Reduce Waste (Buy Right) (opens in new tab), PaintCare, web page, © 2026 PaintCare Inc..
Standards or industry body.
“Most coverage rates are between 300–400 square feed per gallon. If you don’t know the coverage rate, use 350 to get a rough estimate.”
Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 1)
These are summaries of what the sources say, not professional advice. Codes and product data change. Check with your building department and the product label about your own project.
Sources
- [1] PaintCare, Buy the Right Amount of Paint to Reduce Waste (Buy Right). Checked November 12, 2026. https://www.paintcare.org/buy-right/