Paint Calculator
Estimate gallons of paint with coats and door/window deductions.
Result
Enter your room’s length, width and wall height to see how much paint you need.
A 12 × 14 ft room with 8 ft ceilings needs about 3 gallons of paint for two coats.
You’ll need about3gallons
Buy 3 gallons for 2 coats.
- 2 coats
- 350 sq ft/gal
What you’ll need
- Interior paint3 gallonstwo coatsShop interior paint on Amazon (opens in a new tab)
- Roller frame & coversShop paint roller frame and covers on Amazon (opens in a new tab)
- Angled brushfor cutting inShop angled paint brush for cutting in on Amazon (opens in a new tab)
- Paint tray & linersShop paint tray and liners on Amazon (opens in a new tab)
- Painter's tapeShop painter's tape on Amazon (opens in a new tab)
- Drop clothShop canvas drop cloth on Amazon (opens in a new tab)
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Estimated cost
See the full breakdown
- Gross area
- 416.00 sq ft
- Coats
- 2
- Paint needed
- 2.38 gal
- Buy paint
- 3 gal
How this is calculated
- Wall area = 2 × (length + width) × wall height.
- Coverage: 350 sq ft/gal × 1.00 surface factor = 350 sq ft/gal effective.
- Openings: each door 21 sq ft, each window 15 sq ft.
- Gallons = paintable × 2 coats ÷ effective coverage, rounded up to whole gallons.
How much paint do I need?
To figure out how much paint you need, calculate your wall area (2 × (length + width) × wall height for a room), subtract 21 sq ft per door and 15 sq ft per window, multiply by the number of coats, then divide by the paint’s coverage — about 350 sq ft per gallon. For example, a 12 ft × 14 ft room with 8 ft walls, two coats, one door and two windows needs about 2.1 gallons — buy 3 gallons (or 2 gallons plus a quart). Enter your room above for an instant estimate.
How to use this calculator
- Choose what you’re painting. Pick a whole room, a single wall, or the ceiling — that’s what sets the formula.
- Enter your dimensions. Add room length and width (and wall height for walls), or a single wall’s length and height. The calculator derives the area for you.
- Set coats & openings. Keep 2 coats, then enter the number of doors and windows to deduct.
- Read your estimate. See paintable area and the gallons to buy, then share it with a link.
Tips & real-world notes
- A second coat is normal — the calculator defaults to 2. A dark-to-light color change may need 3.
- New drywall and porous masonry drink paint; drop coverage with the surface factor and turn on the primer coat.
- Textured walls and ceilings have more real surface area than their flat footprint — use the surface factor.
- Above about 4 gallons, one 5-gallon bucket is usually cheaper than buying single gallons.
- Primer is a separate product from finish paint — the calculator lists its gallons on their own line so you can buy both.
Frequently asked questions
How much paint do I need for a room?
Find the wall area with 2 × (length + width) × wall height, subtract 21 sq ft per door and 15 sq ft per window, multiply by coats, and divide by 350 sq ft per gallon. A 12 × 14 room with 8 ft walls and two coats needs about 3 gallons.
How much does a gallon of paint cover?
About 350 square feet per gallon for typical interior latex; premium paints claim up to 400. Rough or porous surfaces cover less, so this calculator applies a surface factor.
How many coats of paint do I need?
Two coats are standard for even color and coverage. Plan a third coat when going from a dark color to a much lighter one.
Do I subtract doors and windows?
Yes. This calculator deducts 21 sq ft for each standard door and 15 sq ft for each window from your wall area before estimating gallons.
How much paint for a 12x12 room?
A 12 ft × 12 ft room with 8 ft walls has about 384 sq ft of wall; two coats at 350 sq ft/gal is roughly 2.2 gallons, so buy 3 gallons (or 2 plus a quart).
Do I need primer?
Prime whenever the surface is unsealed or will fight your color: new or patched drywall (raw joint compound and paper soak up paint unevenly), bare wood or masonry, stained or glossy surfaces, and big dark-to-light color changes. Over previously painted walls in a similar color, a quality paint-and-primer usually skips a separate primer. Turn on “Add primer coat” to size one primer coat separately — it covers a bit less than paint (about 200–300 sq ft/gal on porous surfaces), so it’s listed on its own line.
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