How to Calculate Exterior Paint Square Footage for Siding

To calculate exterior siding paint square footage: multiply the house perimeter by the average wall height, add triangular gable areas (1/2 × base × height), subtract 21 sq ft per exterior door and 15 sq ft per window, and multiply by a siding profile factor (1.10 for horizontal lap siding, 1.25 for corrugated metal or cedar shakes, 1.30 for rough stucco).

Painter spraying white acrylic exterior paint on residential wood lap siding with drop cloths

Published 2026-03-01 · Updated 2026-03-01 · 10 min read

Exterior Wall Breakdown & Gable Geometry

Exterior homes feature two distinct wall shapes: rectangular side elevations and triangular roof gables. To compute the total surface area accurately:

1. Rectangular Walls: Length × Wall Height to Eaves.

2. Triangular Gables: 0.5 × Gable Base Width × Gable Peak Height.

3. Subtract large openings: 21 sq ft for standard entry doors, 40 sq ft for double patio sliders, and 120 sq ft for a standard two-car garage door.

Siding Material Texture Multipliers

Horizontal lap siding, board-and-batten, and masonry have contoured surface areas larger than their 2D flat projections. You must apply standard surface multipliers to avoid running out of paint mid-spray:

Worked Example: 2-Story 30×40 ft House with Hardie Lap Siding

Calculating 2 coats of 100% acrylic satin exterior paint for a two-story home with 2 gables, 1 front door, 1 slider, 1 garage door, and 12 windows.

Order 17 total gallons of exterior paint. Using 5-gallon pails reduces costs by ~18% compared to single gallon cans.

How much does weather temperature affect exterior paint coverage?

Standard latex paints require temperatures between 50°F and 90°F. Low-temperature exterior acrylics (like Sherwin-Williams Resilience) can be applied down to 35°F, but coverage thickens slightly.

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