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Paint Calculator

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Enter your room length, width, and ceiling height to find out how many gallons of paint you need — including waste and multiple coats.

1. Enter wall area

Wall area: 384 sq ft (perimeter 48 ft × 8 ft ceiling)

2. Openings to subtract

21 sq ft each (standard 3×7)

15 sq ft each (standard 3×5)

3. Paint type, coats & price

10%
0%10%20%30%
$

Your Paint Estimate

3

gallons

9

quarts total

Calculation breakdown

Gross wall area: 384 sq ft

Openings subtracted: 51 sq ft

Net wall area: 333 sq ft × 2 coats

With 10% waste: 733 sq ft

÷ 350 sq ft/gal = 3 gallons

Coverage varies by paint brand, surface porosity, and application method. Buy a test quart first for new colors.

How to measure for paint

  1. 1. Room dimensions: Measure the length, width, and ceiling height in feet. The calculator computes perimeter × height automatically.
  2. 2. Count openings: Count your standard doors and windows. The calculator subtracts 21 sq ft per door and 15 sq ft per window.
  3. 3. Number of coats: Most rooms need 2 coats for full coverage. Dark colors over light (or vice versa) may need 3.
  4. 4. Paint type: Premium paints cover up to 400 sq ft/gallon. Primers and textured walls need more paint (lower coverage).

Frequently Asked Questions

How many gallons of paint do I need for a 12×12 room?

A standard 12×12 ft room with 8 ft ceilings needs about 1.5 gallons per coat — so 3 gallons for 2 coats. Subtract area for 2 standard doors (~42 sq ft) and 2 windows (~30 sq ft).

How many square feet does a gallon of paint cover?

One gallon of standard latex paint covers 350–400 sq ft per coat on a smooth surface. Primer covers about 250 sq ft. Textured surfaces cover closer to 275 sq ft per gallon.

How many coats of paint do I need?

Most projects need 2 coats. Going from a dark color to a light color may need 3 coats. New unpainted drywall needs 1 coat of primer plus 2 coats of paint.

How do I calculate paint for a room?

Wall area = 2 × (Length + Width) × Height. Subtract ~21 sq ft per door and ~15 sq ft per window. Divide by 350 (coverage per gallon) and multiply by number of coats.

Formula: Gallons = (Wall area − openings) × coats × (1 + waste) ÷ coverage (sq ft/gal). See our methodology page for all constants.