How to use the exterior house paint calculator
- Choose how to enter the walls. Use Area I know if you have the total, or Perimeter and height to build it from the distance around the house, the wall height and the gable ends.
- Enter the doors and windows you will not paint, with the area of one of each. The areas are assumptions you can edit.
- Enter the number of coats and the coverage per gallon from your paint can. Add trim or other area if needed.
- Read the gallons to buy, the area to paint and an optional cost.
Formula
Wall area = distance around x wall height + gables x (1/2 x gable base x gable height), or the area you enter
Area to paint = wall area - doors x door area - windows x window area + trim and other area
Gallons = area to paint x coats / coverage per gallon
Gallons to buy = gallons rounded up to a whole gallon
Coverage per gallon is an example figure you can change. Use the figure on your paint can.
2,000 square feet of walls with 11 openings
A house with 2,000 square feet of wall area, 2 doors of 21 square feet and 9 windows of 12 square feet removes 150 square feet of openings and leaves 1,850 square feet. At 350 square feet per gallon, one coat needs 5.29 gallons, so you buy 6. Two coats need 10.57 gallons, so you buy 11.
Built from measurements, 160 feet around a 9 foot wall with two gables of 30 feet by 8 feet gives 1,440 + 240 = 1,680 square feet. After the same openings 1,530 remain, and two coats need 8.74 gallons, so you buy 9.
Measuring the outside of a house
Walk around the house and measure each wall, or measure the total distance around and use the height from the foundation to the eave. Gable ends, the triangles under a pitched roof, add area that a simple perimeter and height calculation misses, and the tool adds their area with half the base times the height.
Subtract large openings such as garage doors, doors and windows, but you can leave small ones in if you want a little extra for cutting in. Add trim, fascia or shutters as an extra area if you will paint them.
Coverage and what changes it
Paint cans state a coverage per gallon on a smooth surface. Rough siding, brick, stucco and bare wood soak up more paint, so real coverage can be lower than the figure on the can. A primer coat is a separate quantity that this tool does not add.
Waste, spills and touch-ups are not included. For rooms inside, use the paint calculator. For siding material use the siding calculator, for wood protection the deck stain calculator, and for surface areas the square footage calculator.
Assumptions and limits
- Coverage per gallon is an example you can edit and may be lower on rough surfaces.
- Door and window areas are assumptions per opening, and every opening of a type is the same size.
- Gables are triangles, and walls are flat with no extra area for texture or overhangs.
- Primer, waste and trim are not added unless you enter them.
Frequently asked questions
How many gallons of paint do I need for the outside of a house?
Subtract doors and windows from the wall area, multiply by the number of coats and divide by the coverage per gallon, then round up. 1,850 square feet at 350 per gallon is 5.29 gallons for one coat.
How do I measure gable ends?
A gable is a triangle. Multiply half of the base width by the height from the eave line to the peak, then count each gable end.
Does this include primer?
No. Primer is a separate quantity. Run the tool again with the coverage of your primer to estimate it.
Why is the coverage per gallon editable?
Coverage depends on the product and the surface. The figure shown is an example, so use the one on your can and expect less on rough siding.