Paint Calculator

Calculate paint gallons needed for walls, ceiling and trim with cost estimate.

Paintable Wall Area (sq ft)
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Gallons per Coat
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Total Gallons
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Estimated Cost
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Coverage estimate: 350 sq ft per gallon (standard latex paint). Textured or porous surfaces may need more.

How the Paint Calculator Works

This paint calculator computes the paintable wall area by multiplying the room perimeter (2 × length + width) by the ceiling height, then subtracting 21 sq ft per door and 15 sq ft per window for standard openings. The area is divided by 350 — the typical coverage of one gallon of standard latex paint on a smooth primed surface — to get gallons per coat. Total gallons multiplies by the number of coats and is rounded to one decimal place. Multiplying by your price per gallon gives the estimated material cost. Note that rough, textured, or unprimed surfaces absorb more paint and may require 10–20% additional coverage.

Frequently Asked Questions

How much paint do I need for a 12×12 room?
A 12×12 room with 8-ft ceilings has about 384 sq ft of wall area (minus doors/windows ≈ 348 sq ft). That's roughly 1 gallon per coat.
How many square feet does a gallon of paint cover?
Most latex paints cover 350–400 sq ft per gallon on smooth, primed walls. Rough or unprimed surfaces need more.
Do I need primer before painting?
Yes for new drywall, drastic colour changes, or stained walls. Primer seals the surface and improves coverage — often saving a coat of finish paint.
How many coats of paint do I need?
Two coats is standard for most situations. One coat may suffice over similar colours on a well-primed surface.

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