Calculating paint quantities isn\'t as simple as measuring wall area and dividing by coverage. Professional painters use a formula that accounts for wall area(perimeter × height), subtracts openings (doors and windows), and multiplies by the number of coats. A standard gallon of paint covers approximately 350-400 square feet with one coat, but this varies by paint type, surface texture, and application method. Our Room Paint Calculatoruses industry-standard coverage rates adjusted for each paint finish - matte, eggshell, satin, semi-gloss, gloss, and primer all have slightly different coverage characteristics. The calculator also factors in optimal can sizes to minimize waste, since buying paint in the right container sizes can save 10-20% compared to buying all individual gallons.

1. 1. Enter Room Dimensions: Start by selecting your unit system (imperial or metric) and room shape (rectangle, square, or L-shaped). Enter the length, width, and height of your room. For L-shaped rooms, enter the dimensions of the second rectangular section as well. Standard doors subtract ~21 sq ft (1.95 m²) and windows subtract ~15 sq ft (1.4 m²) each.
2. 2. Choose Paint & Application Details: Select your paint type from six finishes (matte through gloss, plus primer), set the number of coats (typically 2 for most projects), and optionally include the ceiling. Enter the price per gallon or liter to see estimated material costs. Toggle the ceiling checkbox if you\'re painting the ceiling with the same paint.
3. 3. Get Recommendations & Buy Smart: The calculator displays total paint needed (in liters or gallons), wall area with openings subtracted, paint required per coat, and estimated cost. The can size recommendation section suggests the most cost-effective combination of quart, gallon, and 5-gallon containers. Use the quick presets to instantly load common room sizes (small bedroom, living room, kitchen, large room).

• Surface Texture: Smooth walls require less paint than textured surfaces (popcorn, stucco, knockdown). Textured walls can absorb 15-20% more paint. If your walls have significant texture, consider adding 1 extra coat or increasing your quantity by 20%.
• Color Change: Painting a dark color over a light wall (or vice versa) often requires an extra coat for full coverage. Drastic color changes may need a primer coat first, which our calculator supports as a paint type option. White paint over white walls may only need 1 coat for touch-ups.
• Paint Quality & Brand: Higher-quality paints typically have better coverage (higher solids content) and may require fewer coats. Budget paints may need 3 coats where premium paint covers in 2. Our calculator uses conservative coverage estimates - adjust the price per unit based on your chosen brand.
• Application Method: Spraying paint uses more paint than rolling or brushing (up to 30% more due to overspray). If you\'re using a sprayer, add 20-30% to the calculated quantity. Rollers with proper nap thickness provide the most efficient coverage for most wall surfaces.

This calculator provides estimates based on standard coverage rates and typical room configurations. Actual paint needs may vary based on surface condition, application technique, paint brand, and environmental factors. Always buy 10-15% more paint than the calculated amount for touch-ups and waste. Most paint stores accept returns of unopened cans, so buying extra is safer than running short mid-project. For professional results, use quality painter\'s tape, drop cloths, and appropriate primer. The calculator supports both imperial (feet/inches) and metric (meters) units - the conversion is automatic when you toggle between systems. All calculations run locally in your browser with no data sent to any server.