CONSTRUCTION · INTERIOR

Paint Calculator

Estimate the gallons of paint needed for your room. Deducts door and window openings and accounts for multiple coats at 400 sq ft per gallon coverage.

LAST REVIEWED · APR 24, 2026 · BY D. MARQUEZ, P.E.
You need
2 gal
Est. cost
$90
Room DimensionsReset
Room length
ft
Room width
ft
Ceiling height8 ft standard
ft
Openings & Coats
Doors21 sq ft each
doors
Windows15 sq ft each
windows
Number of coats2 is standard
Pricing
Price per gallon$35 budget, $65 premium
USD
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How the paint calculator works

The calculator computes wall area from room perimeter × ceiling height, subtracts openings (doors and windows), multiplies by the number of coats, and divides by 400 sq ft per gallon. The result is rounded up to the nearest whole gallon.

How many coats do I need?

  • 1 coat — same-color touch-ups with high-quality paint
  • 2 coats — standard for most color changes (recommended default)
  • 3 coats — light color over dark, or reds/yellows that need extra coverage

Paint quality matters more than you think

Premium paint ($45–$65/gallon) covers better, lasts longer, and is easier to clean than budget paint ($25–$35/gallon). The price difference on a typical room is $20–$60, but premium paint often eliminates the need for a third coat — saving more in time and labor than it costs.

Methodology. Wall area = Perimeter × Height. Paintable area = Wall area - (Doors × 21 sq ft) - (Windows × 15 sq ft). Gallons = ceil(Paintable area × Coats ÷ 400). Standard coverage is 400 sq ft per gallon for smooth surfaces.

Sources

  • Paint coverage: 350–400 sq ft/gallon (Sherwin-Williams, Benjamin Moore specs)
  • Standard door opening: 3×7 ft (21 sq ft)
  • Standard window opening: 3×5 ft (15 sq ft)
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Frequently asked questions

How much paint for a 12×14 room? +
Wall area: 2×(12+14)×8 = 416 sq ft. With 2 doors (-42 sq ft) and 2 windows (-30 sq ft), paintable area is 344 sq ft. At 2 coats: 688 sq ft ÷ 400 = 1.72, so you need 2 gallons.
Does the calculator include ceiling paint? +
No — ceiling paint is typically a separate product (flat white). To calculate ceiling paint, multiply room length × width and divide by 400. A 12×14 room ceiling needs about half a gallon.
How long does interior paint last? +
Quality interior paint lasts 5–10 years in low-traffic areas and 3–5 years in hallways, kitchens, and kids' rooms. Use satin or semi-gloss in high-traffic areas for better durability and easier cleaning.
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