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Paint Calculator

How to Calculate Paint for a Room

Calculating the right amount of paint starts with measuring your room's walls. Multiply the perimeter (2 × length + 2 × width) by the wall height to get the total wall area. Then subtract the area of doors (~21 sq ft each) and windows (~15 sq ft each). The result is your paintable area. Divide this by the paint's coverage rate (typically 350-400 sq ft per gallon for smooth surfaces) and multiply by the number of coats. Most interior rooms need 2 coats for full coverage and color consistency. Adding a 10% waste factor accounts for spills, roller absorption, and touch-ups.

Understanding Paint Coverage Rates

Paint coverage varies significantly based on surface texture and paint quality. Smooth drywall typically gets 350-400 sq ft per gallon, while textured walls may only get 250-300 sq ft per gallon. Rough surfaces like stucco or brick can drop to 150-250 sq ft per gallon. Premium paints generally offer better coverage due to higher pigment concentration. The paint finish also matters: flat paints tend to cover slightly more area than glossy finishes because gloss paints are thinner. Exterior paints typically have coverage rates of 250-350 sq ft per gallon due to weather-resistant formulations being thicker.

Frequently Asked Questions

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

A 12×12 room with 8-foot ceilings has about 384 sq ft of wall area. After subtracting 1 door and 2 windows (~51 sq ft), you have about 333 sq ft of paintable surface. With 2 coats at 350 sq ft/gallon coverage, you need about 1.9 gallons. Buy 2 gallons to account for waste and touch-ups.

How many square feet does a gallon of paint cover?

A gallon of paint typically covers 350-400 sq ft on smooth surfaces with one coat. Textured surfaces reduce coverage to 250-300 sq ft, while rough surfaces like stucco may only get 150-250 sq ft per gallon. These are approximate values — actual coverage depends on paint quality, color, application method, and surface porosity.

Do I need primer before painting?

Primer is recommended when painting new drywall, covering stains, making drastic color changes (especially dark to light), painting over glossy surfaces, or painting porous surfaces like bare wood or masonry. For repainting over the same or similar color on previously painted walls in good condition, most quality paints with built-in primer can skip the separate primer coat.

How many coats of paint do I need?

Most interior painting projects need 2 coats for full, even coverage. You may need 3 coats when covering dark colors with light ones, painting over patches or repairs, using lower-quality paint, or applying paint to new drywall without primer. One coat may suffice for touch-ups with the same color or when using premium one-coat paints.

What paint finish should I use?

Flat/matte is best for ceilings and low-traffic rooms — it hides imperfections. Eggshell works well for bedrooms and living rooms with a subtle sheen. Satin is ideal for family rooms, hallways, and kids' rooms — easy to clean. Semi-gloss is best for kitchens, bathrooms, trim, and doors — moisture resistant. High gloss is used for cabinets, trim accents, and furniture — very durable and easy to clean.

How do I calculate paint for exterior walls?

For exterior walls, calculate the perimeter of your home multiplied by the wall height. Subtract windows and doors. Exterior paint typically covers 250-350 sq ft per gallon due to thicker formulation. Rough surfaces like stucco need more paint. Always add 15-20% waste factor for exterior projects due to wind, overspray, and surface irregularities.