How much paint do I need for a 12x12 room?

A 12x12 room with 8-foot ceilings has approximately 384 square feet of wall area (minus about 50 sq ft for doors and windows, so about 334 sq ft net). With 2 coats at 350 sq ft per gallon, you need about 1.9 gallons — buy 2 gallons. If you are also painting the 144 sq ft ceiling, add another gallon of ceiling paint.

How many square feet does a gallon of paint cover?

A gallon of interior latex paint covers 350 to 400 square feet on smooth, previously painted surfaces. Flat and matte finishes tend to cover closer to 400 sq ft, while satin and semi-gloss cover about 350 sq ft. Porous or textured surfaces like new drywall, rough-sawn wood, or stucco may reduce coverage to 250 to 300 sq ft per gallon.

Should I buy 1-gallon cans or a 5-gallon bucket?

For rooms requiring 3 or more gallons of the same color, a 5-gallon bucket is more economical (typically 15-20% cheaper per gallon) and ensures perfect color consistency. For accent walls or small areas under 2 gallons, individual cans are more practical. Many paint stores also offer quart sizes for small touch-up projects.

How do I calculate paint for ceilings?

Multiply ceiling length by ceiling width to get the square footage. Ceilings typically require one coat of ceiling paint (which is formulated with higher coverage). At 400 sq ft per gallon for ceiling paint, a 12x15 room ceiling (180 sq ft) needs about half a gallon — buy 1 gallon to have extra for touch-ups.

Do I need 2 coats of paint?

Yes, two coats are recommended for virtually all painting projects. The first coat seals the surface and provides a uniform base. The second coat delivers the final color depth, sheen, and durability. The only exception is a touch-up of the exact same color on a previously painted surface, where one coat may suffice.

How much paint do I need for a 1,500 sq ft house interior?

A 1,500 sq ft house typically has 4,000 to 5,000 square feet of paintable wall area (depending on ceiling height and number of rooms). At 2 coats with 350 sq ft per gallon, you need approximately 23 to 29 gallons of wall paint, plus 4 to 5 gallons of ceiling paint. This equates to about 5 to 6 five-gallon buckets total.

Paint Coverage Calculator

How much paint do I need? Free coverage calculator for walls & ceilings — accounts for coats, gives litres and tin count.

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Paint cost calculator: Estimate total project cost by quality level. Free tool for trade to premium — includes supplies estimate in £.

Primer Calculator

How much primer do I need? Free calculator for new plasterboard, timber & repaints — adjusts coverage by surface type.

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How to Use This Calculator

1Measure total wall and ceiling area in square feet (height x width for each wall, then add them up).
2Subtract window and door areas if desired.
3Select the number of coats — 2 coats is standard for most jobs.
4Enter the coverage per gallon from your paint can label (default 350 sq ft).
5Click Calculate Materials to see gallons, cans, and bucket options.

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About This Material

Interior latex paint is the standard finish material for walls and ceilings in residential construction. Coverage rates vary by paint quality and type — flat/matte finishes typically cover 350 to 400 square feet per gallon, while satin, semi-gloss, and high-gloss finishes cover 300 to 350 square feet per gallon due to their thicker consistency. Premium paints from brands like Benjamin Moore Regal Select, Sherwin-Williams Duration, and Behr Marquee often advertise one-coat coverage, but most professional painters recommend two coats for even color and full hide, especially when changing colors. A gallon of paint weighs approximately 10 to 12 pounds when wet. Standard one-gallon cans cost $25 to $70 depending on quality tier, while five-gallon buckets offer significant savings per gallon (typically 15-20% less per gallon). For large projects, buying five-gallon buckets also ensures color consistency across all walls — even within the same color code, individual gallon cans can vary slightly in hue. Ceiling paint is usually a flat white formulated with higher solids for better spatter resistance when rolling overhead. Primer is strongly recommended before the topcoat on new drywall, repaired surfaces, and when making dramatic color changes.

Next Steps:

Paint Cost Calculator →Primer Calculator →

Installation Tips

•Use a 3/8" nap roller for smooth walls, 1/2" nap for light texture, and 3/4" nap for heavy texture or stucco.
•Cut in edges with a 2.5" angled brush before rolling the field.
•Maintain a wet edge — work in 4-foot sections and do not let the edge dry before continuing.
•Apply paint in a W-pattern with the roller, then fill in evenly without lifting the roller.

Common Mistakes to Avoid

Skipping primer on new drywall — bare drywall absorbs paint unevenly, creating flashing and blotchy coverage.
Buying too little paint — running out mid-wall causes visible lap marks where wet and dry paint overlap.
Applying coats too quickly — allow 2 to 4 hours between latex coats for proper drying.
Using cheap rollers — they shed lint and leave texture in the paint film.