Free Paint Calculator
Calculate how many gallons of paint you need for any room. Accounts for doors, windows, and coats with paintable area breakdown.
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Paint Needed
3 gallons
(2.4 exact)
Paintable Area
482 sq ft
Wall Area (total)
560 sq ft
Formula
Paintable Area = 2 × (Length + Width) × Height – (Doors × 21) – (Windows × 12) | Gallons = (Area × Coats) ÷ 400How to Calculate Paint for Any Room
This calculator measures the total wall area of your room, subtracts the space taken up by doors and windows, and divides by the coverage rate (400 square feet per gallon) to tell you exactly how many gallons to buy. It accounts for multiple coats, which is essential for professional-looking results.
Standard door openings are about 21 square feet (3×7 feet) and windows about 12 square feet (3×4 feet). These are industry averages that work for most residential rooms. If you have unusually large picture windows or French doors, you may need to adjust.
Choosing the Right Paint Finish
Paint finish (sheen) affects both appearance and durability. Choosing the right finish for each room makes a big difference:
- Flat/Matte — hides imperfections, ideal for ceilings and low-traffic rooms; hard to clean
- Eggshell — slight sheen, easy to clean; the most popular choice for living rooms and bedrooms
- Satin — soft shine, very washable; great for kitchens, bathrooms, and kids' rooms
- Semi-gloss — noticeable shine, highly durable; best for trim, doors, cabinets, and high-moisture areas
- High-gloss — mirror-like finish, extremely durable; used for doors, furniture, and accent pieces
Paint Preparation Tips
Good prep work is the difference between a paint job that lasts 2 years and one that lasts 10. Clean walls with a damp cloth to remove dust and grease. Fill nail holes and cracks with spackle, sand smooth, and spot-prime patched areas. Use painter's tape on trim, ceiling edges, and around windows for crisp lines.
Remove outlet covers and light switch plates rather than taping around them — it takes less time and gives cleaner results. Lay drop cloths on the floor and over furniture. Cut in corners and edges with a brush first, then roll the large areas.
How to Estimate Paint for Multiple Rooms
If you're painting your whole house one color, add up all the rooms' paintable area and calculate gallons from the total. Buying in 5-gallon buckets saves 10-20% versus individual gallons and ensures color consistency across rooms. For a typical 3-bedroom home, expect to need 8-12 gallons for all walls with two coats.
Frequently Asked Questions
How much paint do I need for a 12×12 room?
A 12×12 room with 8-foot ceilings, 1 door, and 2 windows has about 525 square feet of paintable wall area. With 2 coats, you need about 2.6 gallons — so buy 3 gallons. For the ceiling, add another gallon.
How many square feet does a gallon of paint cover?
One gallon of paint covers approximately 350-400 square feet on smooth surfaces. Textured walls, bare drywall, or porous surfaces absorb more paint and may only get 250-300 sqft per gallon. This calculator uses 400 sqft/gallon as the standard.
Do I really need two coats of paint?
Almost always, yes. Two coats ensure even color, hide old colors showing through, and provide better durability. The exception is if you're repainting the same color or using a high-quality paint-and-primer combo over a similar shade. Dark-to-light color changes may need 3 coats.
How much does it cost to paint a room?
DIY painting a 12×12 room costs $100-$200 for quality paint, primer, tape, and rollers. Professional painters charge $300-$800 per room depending on size, prep work needed, and your area. Paint itself runs $25-$50 per gallon for mid-range quality.
Should I use primer before painting?
Use primer when painting over dark colors, new drywall, patched areas, stains, or glossy surfaces. A separate primer is cheaper per gallon than paint-and-primer combos and blocks stains better. For repainting similar colors over clean, previously painted walls, you can skip primer.