Paint Coverage Calculator

Paint Coverage Estimation

Paint coverage depends on paint type, surface, and coat count.

The can says 400 square feet. That is a lab figure, rolled by a machine onto a sealed panel. Once you allow for cutting in, roller absorption, and a wall that drinks the first coat, 350 is the working number for standard interior latex, and it is the figure the room paint coverage calculator uses too. Both pages now start from the same coverage table, so the same job gets the same answer whichever one you open.

Standard coverage (smooth drywall, primed):

Stain is the one to distrust. A weathered cedar deck can swallow a gallon in 150 square feet while a sealed one gives you 300, and no calculator can tell which you have until you start. Buy for the low end of that range.

Surface adjustments:

The factor multiplies coverage, so a 0.5 factor halves the square feet a gallon does, which means twice the paint. Easy figure to get backwards, and getting it backwards on brick costs you a second trip.

Number of coats:

• Same color, same brand: 1 coat usually fine
• Same color over light to medium tint: 2 coats recommended
• Light over dark: 2-3 coats + primer
• Dark over light: 1-2 coats with quality paint
• Bright / saturated colors (red, yellow): 3+ coats often needed

Calculation: Gallons = (Total area × Coats) / (Coverage per gallon × Surface factor)

Standard room measurements:

These are gross wall areas, from 2 × (length + width) × height. The box above wants the net figure, so take the openings off these before you type one in.

Subtract for openings:

• Standard interior door: 20 sq ft
• Window: 15 sq ft
• Sliding glass door: 40 sq ft
• Bi-fold closet door: 12 sq ft

Those are the same deductions the room calculator applies automatically, so the two pages land on the same net area for the same room.

Exterior considerations:

• Add 10% for waste, drips, brush rinses
• Add 20-30% for first-coat primer on raw siding
• Plan two coats for fade-prone exposures (south, west)

Cost ranges (US, 2026):

• Builder-grade interior latex: $20-30/gallon
• Mid-range (Behr, Sherwin-Williams ProMar): $35-50/gallon
• Premium (Benjamin Moore Aura, SW Emerald): $60-90/gallon
• Specialty (chalkboard, magnetic, fire-rated): $40-100/gallon

This page or the room one?

Use this page when you already have a square footage and the surface is not plain drywall. It is the one that handles brick, stucco, raw wood, a deck, a fence, or an exterior wall, because it carries the surface factor and the stain and masonry coverage rates. Anything you measured yourself with a tape belongs here.

Use the room paint coverage calculator when you have not measured yet. Give it length, width, height and a count of doors and windows, and it works the area out, offers the ceiling as an option, and shows how much of the wall the openings actually take. It is the faster route for one interior room. Both use the same coverage figures and the same 10% waste, so they agree on the answer.