How much paint do I need for a room?

To calculate paint needed: 1) Measure room length, width, and height, 2) Calculate wall area = (2 × length + 2 × width) × height, 3) Subtract doors (21 sq ft each) and windows (15 sq ft each), 4) Divide by coverage rate (typically 350-400 sq ft per gallon), 5) Multiply by number of coats. For example, a 12×15 ft room with 8 ft ceilings needs approximately 2-3 gallons for 2 coats.

How much area does one gallon of paint cover?

One gallon of paint typically covers 350-400 square feet per coat on smooth surfaces. Coverage varies based on: surface texture (rough surfaces use more paint), paint quality (premium paints often cover better), application method (spraying uses more than rolling), and surface porosity (new drywall absorbs more paint). Always check the manufacturer's coverage rate on the paint can.

Do I need primer before painting?

Primer is recommended when: painting new drywall or bare wood, making dramatic color changes (especially dark to light), covering stains or marks, painting over glossy surfaces, or using a significantly different paint type. Primer improves paint adhesion, provides uniform coverage, and can reduce the number of paint coats needed. For minor repaints in similar colors, primer may not be necessary.

What is the difference between latex and oil-based paint?

Latex (water-based) paint: dries quickly (1-2 hours), easy cleanup with water, low odor, flexible and breathable, ideal for most interior walls. Oil-based paint: takes 6-8 hours to dry, requires mineral spirits for cleanup, stronger odor, more durable finish, better for high-traffic areas and trim. Most homeowners prefer latex for walls due to ease of use and lower VOCs.

Paint Calculator - Calculate Paint Needed for Your Room | AICalculator

How to Calculate Paint for Your Room

Calculating the right amount of paint ensures you have enough to complete your project without excessive waste or multiple store trips. Our paint calculator makes this process simple and accurate.

Paint Coverage Basics

Standard Coverage Rates

• Smooth walls: 400 sq ft per gallon
• Average texture: 350 sq ft per gallon
• Rough/textured walls: 300 sq ft per gallon
• Primer: 350-400 sq ft per gallon
• Ceiling paint: 350-400 sq ft per gallon

Step-by-Step Calculation

Measure Your Room: Measure length, width, and height in feet or meters
Calculate Wall Area: (Length + Width) × 2 × Height = Total wall area
Subtract Openings: Deduct doors (21 sq ft each) and windows (15 sq ft each)
Determine Paint Needed: Divide net area by coverage rate (usually 350 sq ft/gallon)
Multiply by Coats: Most projects need 2 coats for best results
Add Extra: Buy 10-15% extra for touch-ups and future repairs

Example Calculation

12' × 15' Room with 8' Ceilings

1. Wall perimeter: (12 + 15) × 2 = 54 feet

2. Total wall area: 54 × 8 = 432 sq ft

3. Subtract 1 door (21 sq ft) and 2 windows (30 sq ft): 432 - 51 = 381 sq ft

4. Paint for 1 coat: 381 ÷ 350 = 1.09 gallons

5. Paint for 2 coats: 1.09 × 2 = 2.18 gallons

✓ Buy 2.5-3 gallons for this room

Paint Types Comparison

Feature	Latex (Water-Based)	Oil-Based
Drying Time	1-2 hours	6-8 hours
Cleanup	Soap and water	Mineral spirits
Odor	Low/Minimal	Strong
Durability	Good	Excellent
Best For	Walls, ceilings	Trim, doors, cabinets

When to Use Primer

✅ Primer Recommended

• New drywall or plaster
• Bare wood surfaces
• Dark to light color changes
• Covering stains or marks
• Glossy surfaces
• Porous surfaces (brick, concrete)

⚠️ Primer Optional

• Previously painted walls in good condition
• Similar color repainting
• Using paint + primer combo
• Light to dark color changes
• Touch-up work

Professional Painting Tips

Buy Quality Paint: Premium paint covers better and lasts longer, often requiring fewer coats
Two Thin Coats: Better than one thick coat for even coverage and durability
Keep Extra Paint: Store leftover paint for touch-ups (label with room name and date)
Proper Preparation: Clean walls, fill holes, and sand for best results
Use Right Tools: Quality brushes and rollers make application easier and smoother
Test Colors: Buy sample sizes to test colors before committing to full gallons
Calculate Ceiling Separately: If painting ceiling, calculate its area separately

Cost Considerations

Paint costs vary widely based on quality and brand. Budget paint costs $15-25 per gallon, mid-range paint costs $25-40 per gallon, and premium paint costs $40-80+ per gallon. While premium paint costs more upfront, it often provides better coverage, requiring fewer coats and less total paint, potentially saving money overall.

Don't forget additional costs: primer ($20-30/gallon), painter's tape ($5-10), drop cloths ($10-20), brushes and rollers ($15-30), and paint trays ($5-10). For professional painting, labor typically costs 2-3 times the material cost.