About this tool
This exterior paint calculator estimates body paint, trim paint, and primer for a whole house. Measure either the perimeter or the four sides, give the wall height per story and the number of stories, add gable ends as triangles, and subtract doors, windows, and garage doors. A texture factor scales the area up for surfaces that hold more paint: smooth fiber cement or aluminum siding at 1.0, wood clapboard or textured hardboard at 1.2, and stucco, brick, or rough-sawn siding at 1.5. Trim is entered as linear feet and converted to area at half a square foot per foot, then figured separately because trim is usually a different color and sheen. It is for homeowners budgeting a repaint, painters double-checking a bid, and anyone deciding between two and three coats.
How it works
Body area = perimeter x wall height x stories + sum of gables (each 1/2 x width x height) - doors x 21 sq ft - windows x 15 sq ft - garage doors x 112 sq ft. That net area is multiplied by the texture factor (1.0, 1.2, or 1.5), by the number of coats, and by 1 + waste%, then divided by the coverage rate, 400 sq ft per gallon by default for exterior acrylic latex on a sealed surface. Trim area = linear feet x 0.5 sq ft/ft (a typical 4 to 6 inch face plus edges), figured at the same coverage. Primer is one coat over the textured body area and trim at its own rate, 300 sq ft/gal by default. Gallons round up to whole cans and split into 5-gallon buckets and 1-gallon cans. Metric mode converts meters to feet internally and reports liters at 3.785 L per gallon.
Frequently asked questions
How many gallons of paint does it take to paint a house exterior?
A 1,500 sq ft single-story ranch with about 1,300 sq ft of net siding needs roughly 7 gallons for two coats at 400 sq ft per gallon, plus one or two gallons of trim paint. A 2,500 sq ft two-story colonial typically needs 15 to 20 gallons of body paint. Stucco and rough wood push those numbers up by 20 to 50 percent because the texture holds more paint, which is what the texture factor models.
What is the texture factor and which one should I use?
Coverage figures on the can assume a smooth, sealed surface. Texture adds real surface area and soaks up paint in the low spots. Use 1.0 for smooth fiber cement, vinyl, aluminum, or previously painted smooth wood; 1.2 for wood clapboard, textured hardboard, or lightly textured stucco; 1.5 for heavy stucco, split-face block, brick, or rough-sawn cedar. When unsure, use the higher factor for the first coat estimate and adjust after the first wall.
Do I need primer on exterior siding?
Prime bare wood, new fiber cement without factory primer, patched areas, chalky or weathered paint, and any surface where you are changing from a dark to a light color. Sound, previously painted siding that has been washed usually does not need a full coat of primer under a quality self-priming exterior paint; spot-prime repairs instead. When you tick the primer box, the calculator figures one coat over the whole body and trim so you have the upper bound.
How do I measure gables?
A gable is the triangle of wall between the top of the side wall and the roof peak. Measure its width at the base (the same as the wall below) and its height from the top of the wall to the peak; the area is one half of width times height. A 30 ft wide gable rising 8 ft to the peak is 120 sq ft. Most houses have two matching gables; hip roofs have none, and cross-gabled houses may have three or four.