Exterior Paint Calculator

Gallons = wall and gable area, less doors and windows, × coats ÷ 400 sq ft a gallon: a 30 × 9 ft wall under a 6 ft gable, with a door and two windows, is 318.67 sq ft, or 2 gallons for two coats.

Your measurements

Example

Use the unit shown for each box, or type another one: 12 ft 6 in, 150 in, 3.8 m and 600 mm all work, as do the marks on a tape measure.

Elevation 1

Wall width (ft) Wall height (ft) Gable rise (ft) Doors Count them. The door size is in the details below. Windows Other openings you measured (sq ft) An archway, a patio door or any opening not counted above.

Measure from Paint coats

Details Package sizes, prices and materials

Extra paint (%) Door width A common door width from a door maker. Change it to your door. Door height 80 inches is the standard door height in rooms with 8-foot ceilings. Window width Window height 32 × 48 inches is one standard window size. Measure yours for a closer answer. Coverage per gallon (sq ft) Can size (gal) Your price per can ($)

Example: replace these measurements

Your material list

2 1-gallon paint cans

318.67 sq ft measured

Your measured layout

Wall elevation with a triangular gable above the dashed line. Openings are subtracted separately.

Your shopping list

2 1-gallon paint cans

Already have some? See what it covers

How many 1-gallon paint cans you have

Quantities and package details

Paintable area: 318.67 sq ft
Openings deducted: 1 door, 2 windows: 41.33 sq ft
Area across all coats: 637.33 sq ft
Paint before can rounding: 1.59 US gal
Paint volume before rounding: 6.03 liters
Surface 1: 318.67 sq ft

The calculation

Surface area: 318.67 sq ft
ceil(318.666667 × 2 × (1 + 0/100) ÷ 400) = 2

Common questions

How do I measure a house for paint?

Treat each wall as a rectangle and add the triangle of any gable above it: half the wall width times the gable rise. Count the doors and windows on each wall so they are subtracted.

How much paint does a house need?

Add the walls, subtract the openings, multiply by the coats and divide by the coverage on the can. Rough siding takes more paint than the label’s figure for a smooth surface.

Source: Sherwin-Williams paint questions. Listed on the Sources page.

Should trim be on the same list?

Keep trim, doors and shutters on a separate list; they usually take a different finish.

How to plan the quantity

Each elevation combines a rectangle and an optional triangular gable above it. The gable rise is its height above the rectangle. Set that rise to zero for a plain wall.

Count the doors and windows on each wall; their sizes are in the details and can be changed. Add any other opening you measured in square feet. Add another elevation for a different wall, and keep trim or a different color on a separate list.

The calculation multiplies the net area by your coats and divides by product coverage. Rough or porous siding can need a different coverage input from smooth trim.

Before you order

Access equipment, cleaning, scraping, repairs and lead-safe work can matter more than the paint quantity. This list does not price those tasks.
Use the product’s guidance for the substrate and application method. A geometric area is not a promise of real-world coverage.

Have prices moved?

Paint cost 5.9% more in August 2026 than a year earlier (Bureau of Labor Statistics producer price index, preliminary).

Before ordering, read the guide: How much paint do I need? Coverage, coats and primer. Or choose another calculator.