Paint Calculator: Complete Guide
This paint calculator helps you figure exactly how much paint you need for your project — including walls, ceilings, and trim. Enter your room dimensions and get results in gallons, liters, and total cost.
🎨 Quick Formula: Wall Area = 2 × (Length + Width) × Height - (Window Area + Door Area)
Example: 15' × 12' room with 8' ceilings, 2 windows, 1 door
Total wall area = 2 × (15+12) × 8 = 432 sq ft
Subtract windows (2 × 15 = 30 sq ft) and door (1 × 20 = 20 sq ft)
Net area = 432 - 50 = 382 sq ft
At 350 ft²/gal with 2 coats: 382 × 2 ÷ 350 = 2.18 gallons
How Much Paint Do You Need?
Paint coverage varies by surface type, paint quality, and application method. Here are general guidelines:
- Smooth drywall: 350-400 sq ft per gallon
- Textured walls: 250-300 sq ft per gallon
- Ceilings: 300-350 sq ft per gallon
- Trim and baseboards: 400-500 sq ft per gallon
- Exterior siding: 250-350 sq ft per gallon
Always add 10-15% extra for touch-ups, waste, and unexpected coverage issues.
Real-World Painting Examples
- Small bedroom (10' × 10', 8' ceilings): Walls: 1.2 gal, +Ceiling: 1.7 gal total
- Living room (15' × 12', 8' ceilings): Walls: 1.8 gal, +Ceiling: 2.5 gal total
- Large master (18' × 16', 9' ceilings): Walls: 2.8 gal, +Ceiling: 4.0 gal total
- Whole house (2,000 sq ft): 12-15 gallons (walls + trim)
📋 Real Project: Living Room & Kitchen Repaint
Project: Open concept living room + kitchen, Austin, TX | Area: 20' × 25' (500 sq ft)
📐 Calculations:
Room dimensions: 20' × 25' × 9'
Wall area: 2 × (20+25) × 9 = 810 sq ft
3 windows (45 sq ft), 2 doors (40 sq ft)
Net wall area: 810 - 85 = 725 sq ft
Ceiling area: 20 × 25 = 500 sq ft
Total area: 725 + 500 = 1,225 sq ft
2 coats: 1,225 × 2 = 2,450 sq ft
At 350 ft²/gal: 7.0 gallons
Cost: 7 × $45 = $315
5 Common Paint Calculation Mistakes
- Forgetting to subtract windows and doors: Standard window = 15 sq ft, door = 20 sq ft.
- Not accounting for multiple coats: Most rooms need 2 coats for even coverage.
- Ignoring texture: Textured surfaces absorb more paint — reduce coverage by 20-30%.
- Buying exact amount: Always buy 10-15% extra for touch-ups.
- Using the wrong coverage value: Different paints have different coverage — check the label.
🔧 Paint Troubleshooting
Common paint estimation problems and solutions.
❌ "I ran out of paint before finishing"
→ You likely under-estimated coverage or forgot to account for texture. Always buy 10-15% extra.
❌ "I bought too much paint"
→ Many stores accept returns on unopened cans. Plan ahead and buy from a store with a return policy.
❌ "The color looks different on the wall"
→ Always test a small area first. Lighting and surface texture affect color perception.
Frequently Asked Questions
How much paint do I need for a 12×12 room?➕
For a 12' × 12' room with 8' ceilings: walls = 384 sq ft, ceiling = 144 sq ft. With 2 coats: ~2.5-3 gallons total (walls + ceiling).
How many square feet does a gallon of paint cover?➕
Most paints cover 350-400 sq ft per gallon on smooth surfaces. Textured surfaces reduce coverage to 250-300 sq ft per gallon.
Should I include trim in my paint calculation?➕
Yes, trim (baseboards, crown molding, door frames) adds to the total area. A gallon of trim paint covers 400-500 sq ft.
How much paint for a 2,000 sq ft house?➕
For interior walls only: 10-12 gallons for 2 coats. Including ceilings and trim: 15-18 gallons total.
Can I use this calculator for exterior painting?➕
Yes! For exterior surfaces, use 250-350 sq ft per gallon depending on siding type. Add 15% for waste due to spraying.
