Outside Paint Calculator
A house exterior looks uniform from the curb, but every square foot of siding, trim, and soffit adds up fast. Use this outside paint calculator to convert your home's perimeter and wall height into a gallon estimate, accounting for siding texture and the doors and windows you won't be painting. The result tells you exactly how many gallons of outside paint to buy and what it will cost at your chosen grade.
How Much Outside Paint Do You Need
The formula converts your home's perimeter and wall height into gross wall area, subtracts door and window openings, then divides by coverage per gallon. One gallon of exterior acrylic covers about 300 square feet on smooth siding and less on rougher surfaces.
| Siding | Coverage per gallon |
|---|---|
| Fiber cement (smooth) | 300 sq ft |
| Vinyl or wood lap | 273 sq ft |
| Rough sawn / board and batten | 214 sq ft |
| Stucco | 231 sq ft |
| Brick or CMU | 222 sq ft |
Measuring Your Home Exterior
Walk the perimeter of your house with a tape measure or pace it off if you already know the footprint. A rectangular 40x30 ft home has a perimeter of 140 linear feet. Multiply by wall height: 9 ft for a single-story to the eave, 18-20 ft for a two-story. That gives you gross wall area.
Subtract 21 sq ft for each exterior door and 15 sq ft for each standard window. The result is your paintable area.
Worked Example
A 2,000 sq ft two-story with a 160 ft perimeter and 18 ft walls has 2,880 sq ft gross wall area. Subtract 2 doors (42 sq ft) and 12 windows (180 sq ft) and you're left with 2,658 sq ft of paintable siding. For two coats on lap siding (273 sq ft/gal effective), that's 2,658 x 2 / 273 = 19.5 gallons. Order 20 gallons.
Paint Grade Economics
Premium exterior paint costs $80/gal but carries a 25-year warranty and actually lasts 15-20 years in real use. Economy paint at $30/gal lasts 5-7 years. On a 20-gallon job, premium costs $1,000 more upfront but saves you from repainting in 5 years. For any home you plan to keep, premium is the cheaper long-term choice.
When to Paint Outside
Paint when the surface and air temperature are both 50-85 degrees F, humidity is below 85%, and no rain is forecast for 24 hours. Avoid midday sun on hot days. Spring and early fall hit these conditions most reliably in most climates.
Prep Is Half the Job
Pressure wash first to remove chalking, mildew, and loose paint. Scrape any peeling areas, spot-prime bare wood, and caulk gaps around trim and windows. Skipping prep is the single biggest reason exterior paint jobs fail early.