Paint Calculator

For a 12×12 foot (3.7×3.7 m) room with 8-foot (2.4 m) ceilings, wall area is approximately 384 sq ft (35.7 m²). Subtract ~50 sq ft (4.6 m²) for a door and two windows, leaving 334 sq ft (31 m²). With two coats at 350 sq ft/gallon coverage, you need approximately 2 gallons (7.6 liters) for walls. Add 1 gallon (3.8 L) for the 144 sq ft ceiling. Total: about 3 gallons (11.4 liters) for complete room coverage.

Most paint jobs require two coats for proper coverage, color depth, and durability. One coat often shows brush marks, roller lines, and uneven coverage. Three coats are needed when: painting light colors over dark, covering stains, or painting bare drywall without primer. Premium "one-coat" paints may achieve coverage on primed surfaces, but two coats always provides better durability and appearance. Always use primer on new surfaces or when changing from dark to light colors.

For L-shaped or irregular rooms, measure each wall separately and add them together. Multiply each wall's length by height. For vaulted ceilings, calculate triangular portions separately using ½ base × height. Subtract 20 sq ft (1.9 m²) per standard door and 15 sq ft (1.4 m²) per average window. Don't subtract for windows under 10 sq ft—extra paint covers trim and touch-ups. Add all wall areas together for total paintable surface.

Several factors reduce coverage below manufacturer's stated rates. Textured surfaces like stucco or popcorn ceilings absorb more paint, reducing coverage by 20-30%. Porous surfaces like bare wood or unsealed drywall need more paint. Dark colors require heavier application. Application method matters: spraying uses 20-25% more paint than rolling due to overspray. High humidity, extreme temperatures, and improper thinning also affect coverage and drying times significantly.

Interior latex paint prices vary globally: USA $25-60/gallon for quality brands; UK £25-55 per 2.5L; EU €30-70 per 2.5L; Australia A$50-100 per 4L; India ₹200-600/liter. Premium and specialty paints cost 2-3× more. Primer costs slightly less. Budget brands offer lower prices but often require additional coats. Professional-grade paints provide better coverage, durability, and often cost less per square foot due to superior spreading rates.

Use primer when: painting new drywall or bare wood, covering stains or odors, changing from dark to light colors, painting over glossy surfaces, or switching paint types (oil to latex). Primer costs less than paint and improves adhesion, coverage, and final appearance. Self-priming paints work for repainting similar colors on previously painted surfaces in good condition. For best results, tint primer toward your finish color when making dramatic color changes.

One US gallon equals 3.785 liters. One liter equals 0.264 gallons. Common paint can sizes: USA uses 1 gallon (3.8L) and quarts (0.95L); UK/Europe uses 1L, 2.5L, and 5L; Australia uses 1L, 2L, 4L, and 10L. Coverage is often listed as sq ft per gallon (US) or m² per liter (metric). To convert: 350 sq ft/gallon ≈ 8.6 m²/liter. This calculator automatically converts between systems.

Latex/acrylic paints typically require 2-4 hours between coats in normal conditions (20°C/68°F, 50% humidity). Oil-based paints need 24 hours. High humidity, low temperatures, or poor ventilation extend drying times significantly. Paint should feel dry to touch and not tacky before recoating. Applying second coat too soon causes peeling, bubbling, and uneven finish. In humid conditions or basements, wait longer—overnight is safest for critical projects.