How Many Gallons to Paint Exterior House: Real Estimates: 1 Minute to Calculate How Much Paint You Really Need for Exterior Walls

Wondering “how many gallons to paint exterior house”? You’re not alone—getting this right can mean the difference between a flawless finish and costly mistakes. As a seasoned interior designer, I’ve calculated paint for everything from modern townhomes to sprawling bungalows, and precision always pays. Here’s the framework I use to dial in that magic number with confidence for every exterior project.

First rule: Base your estimate on total wall square footage, surface texture, and desired number of coats. Most professionals rely on 1 gallon covering 350–400 square feet per coat, as verified by the National Association of Home Builders (see NAHB coverage recommendations). For my last client—a two-story, 2,400 sq ft Colonial—we started with a digital floor plan creator to measure precisely. It was worth every minute: no overbuying, no second trips to the hardware store, and a cleaner final result.

Key detail: Subtract windows and doors (about 20 sq ft each) to get your true paintable surface area. If your home has textured finishes (stucco, shingles, rough wood), increase your gallon estimate by 10–15% to account for extra paint absorption. Don’t forget color—you’ll need more paint for bold color changes or switching from dark to light shades. Based on American Institute of Architects (AIA) guidance, planning for two full coats ensures longevity and even coverage, meeting both aesthetic and durability standards (AIA exterior repaint tips).

Tips 1: The Essential Math for Paint Estimation

The core equation is straightforward:

1. Calculate total wall square footage (length × height × number of walls).

2. Subtract unpainted areas (windows, doors).

3. Multiply by the number of coats.

4. Divide by paint coverage per gallon (found on the can, usually 350–400 sq ft).

Want pro-level precision? Use a free 2D floor planner—they’ll tally it all automatically. For my last Victorian home repaint, the planner helped us spot a calculation error before we started, saving both money and time.

Tips 2: Avoid These Gallon-Estimation Pitfalls

Skipping texture adjustments is the #1 mistake. Wood and unfinished masonry “drink” more paint, so ignoring this can leave you short by as much as 20%. The U.S. Department of Housing and Urban Development (HUD) also recommends always rounding up by 10% to allow for touch-ups (HUD painting guide).

And climate matters: Hot or windy conditions can speed up paint drying, leading to less spread per gallon. I’ve seen a 20% coverage drop in Arizona’s dry heat, while coastal weather does the opposite—slower drying, slightly better spread but longer project times.

Tips 3: Client Story—Getting it Right the First Time

Last spring, my client Laura wanted to repaint her historic Craftsman. She guessed six gallons would work, but after a full surface audit—including her home’s heavy stucco texture and two color changes—we tallied 10 gallons. The result? Flawless coverage, zero patchiness, and only half a gallon left for future nicks. By using a 3D exterior visualizer, we even previewed accent colors and confidently avoided overbuying.

Tips 4: Pro Pointers for a Smooth Exterior Paint Experience

1. Always check the coverage spec—paint types vary, so don’t assume every brand coats the same.
2. Factor in paint and primer—bare wood and unprimed masonry absorb more, sometimes double.
3. Leave a buffer—an extra 10% is a safety net for future touch-ups and repairs.
4. Use digital tools—let floor planners and coverage calculators do the heavy lifting and improve your cost predictability.

Tips 5: Make It Easier—Recommended Estimation Tools

Here are a few trusted tools:

1. Coohom Free Floor Plan Creator – For quick digital wall measurements.
2. Ace Hardware Paint Calculator – Simple online estimator.
3. Sherwin-Williams Paint Calculator – Includes texture and number of coats.

FAQ

How do I calculate how many gallons to paint exterior house?

Multiply your home's paintable wall area by number of coats, subtract windows/doors, and divide by the recommended coverage per gallon (usually 350–400 sq ft). Add a 10% buffer for touch-ups.

Do rough surfaces need more paint?

Absolutely. Plan on 10–20% extra for stucco, unpainted wood, or textured siding.

What if I'm switching from dark to light colors?

You'll almost always need an extra coat to prevent show-through. Use a premium primer if possible.

Does climate affect paint coverage?

Yes—humidity, temperature, and wind all impact how well paint spreads and dries. In extreme climates, you may require extra gallons or longer drying times.

How can I avoid running out of paint?

Let a digital calculator help, always round up to the next gallon, and buy an extra quart for unforeseen touch-ups.