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Paint Calculator
Paint Calculator
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Paint Calculator

Calculate gallons of paint needed for any room, including doors and windows.

DIY difficulty

EasyTypical time: 1–2 days per room
  • ›Prep work (taping, patching, priming) takes most of the time
  • ›Rolling technique is learnable in minutes
  • ›Cutting in at edges and trim is where most people struggle

Must-have tools

Roller + extension poleAngled brush for edgesPainter's tapeDrop cloths

How to calculate how much paint you need

  1. Measure each wall's length and height. Entering the room length and width works too — the calculator treats all four walls.

  2. Enter the ceiling height, number of doors, and number of windows. Doors subtract about 20 sq ft each; windows subtract about 15 sq ft.

  3. Choose the number of coats. Fresh drywall or drastic color changes usually need two. Touch-ups and same-color repaints often need just one.

  4. Read the gallons needed and round up to the next full gallon. A little leftover is useful for future touch-ups.

Common uses

  • Painting a bedroom, living room, or kitchen before moving in
  • Estimating paint for a whole-house interior refresh
  • Budgeting material costs for a rental property turnover

Frequently asked questions

How much area does a gallon of paint cover?
Most interior paints cover 350–400 square feet per gallon on a smooth, primed surface. Rough or porous surfaces absorb more — plan for 300 sq ft per gallon.
Do I need a primer before painting?
Yes, on new drywall, bare wood, or when making a big color change. Primer improves coverage and adhesion, and can reduce the number of finish coats you need.
How much paint do I need for a 12×12 room?
A standard 12×12 room with 8-foot ceilings, two doors, and two windows needs about 1.5 gallons for one coat — call it 2 gallons to be safe.
How long should paint dry between coats?
Most latex paints need 2–4 hours between coats at 70°F and 50% humidity. Oil-based paints need 24 hours. Always follow the label — rushing coats causes peeling and uneven sheen.
How many gallons of paint do I need for a 1,500 sq ft house interior?
A typical 1,500 sq ft home with 8-foot ceilings has roughly 2,500–3,000 sq ft of paintable wall area. At 350 sq ft/gallon with two coats, expect 15–20 gallons for walls only.

Common mistakes to avoid

  • ✕Skipping primer on new drywall — fresh drywall absorbs the first coat unevenly. PVA primer is mandatory on new drywall.
  • ✕Underestimating coverage on textured or dark walls — 400 sq ft/gallon assumes smooth, primed surface. Rough texture cuts coverage to 250–300 sq ft/gallon.
  • ✕Buying different sheen levels by accident — mixing sheens on the same wall creates visible variation under certain lighting.
  • ✕Not accounting for trim, ceiling, and accent colors separately — the calculator estimates walls only.

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Not sure whether to DIY this project?

Read our project-by-project guide on when to hire a contractor vs. do it yourself.

Read the guide →

About this calculator

Enter room dimensions, ceiling height, number of doors and windows, and number of coats to get the exact gallons of paint you need. Accounts for standard door and window sizes.

All results are estimates. Verify quantities with your local supplier and confirm measurements before purchasing materials. Requirements vary by region and project type.

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