Construction & Engineering
Paint Calculator
Use our free Paint Calculator to estimate the amount of paint needed for your walls, ceilings, or rooms. Save time and money by calculating accurate paint coverage before your project.
Why Use a Paint Calculator?
Buying too much paint wastes money; buying too little means extra trips to the store and potential color-batch mismatches. Whether you're painting a single accent wall or an entire house, accurate estimation saves time, money, and frustration.
This calculator computes the exact paintable area for walls, ceilings, and trim — automatically deducting doors and windows. It tells you how many gallons (or liters) you need based on paint type, coverage rate, and number of coats.
How to Use This Calculator
- Select paint type and number of coats
- Check which areas to paint (walls, ceiling, trim)
- Enter room length, width, and ceiling height
- Enter number of doors and windows to deduct
- Click Calculate Paint Needed
Common Use Cases
- Bedroom & living room
- Kitchen & bathroom
- Exterior walls
- Accent walls
- Ceiling repaints
- Trim & baseboard
Paint Coverage Reference
| Paint Type | Coverage (ft²/gal) | Coverage (m²/L) | Best For |
|---|---|---|---|
| Interior Latex | 350 – 400 | 8 – 10 | Walls, bedrooms, living rooms |
| Exterior Latex | 250 – 350 | 6 – 9 | Siding, fences, outdoor walls |
| Primer | 250 – 350 | 6 – 9 | New drywall, bare wood, stain blocking |
| Ceiling Paint | 350 – 450 | 8 – 11 | Ceilings (thicker, less drip) |
| Semi-Gloss | 350 – 400 | 8 – 10 | Trim, doors, kitchens, bathrooms |
| High-Gloss | 300 – 350 | 7 – 9 | Cabinets, furniture, accents |
Coverage varies by surface texture, porosity, and application method. Rough or porous surfaces require more paint.
Standard Deductions
| Item | Standard Size | Area Deducted |
|---|---|---|
| Interior Door | 3' × 6'8" | ~20 ft² |
| Standard Window | 3' × 5' | ~15 ft² |
| Sliding Glass Door | 6' × 6'8" | ~40 ft² |
| Large Picture Window | 5' × 5' | ~25 ft² |
This calculator uses 20 ft² per door and 15 ft² per window. For non-standard sizes, adjust the count accordingly.
FAQ – Paint Calculator
What is a Paint Calculator?
A Paint Calculator estimates how much paint you need to cover walls, ceilings, and trim based on room dimensions, paint type, and number of coats. It deducts doors and windows for accuracy.
How does the calculator handle doors and windows?
Each standard door deducts ~20 ft² and each window deducts ~15 ft² from the total wall area. This prevents you from overbuying paint for areas that won't be painted.
How many coats of paint do I need?
Most projects need 2 coats for even coverage. Use 1 coat for touch-ups or same-color refreshes. Use 3 coats when covering dark colors with light paint or on porous surfaces.
What's the difference between interior and exterior paint?
Exterior paint is formulated to resist UV, moisture, and temperature changes. Interior paint focuses on washability and low odor. They have different coverage rates — exterior typically covers less per gallon.
Do I need primer?
Primer is recommended for new drywall, bare wood, stain blocking, or when making dramatic color changes. It improves adhesion and can reduce the number of topcoats needed.
How is trim area calculated?
Trim includes baseboards (room perimeter × 0.5 ft) plus door and window casings. It's typically a small fraction of total area but uses different paint (usually semi-gloss).
Should I buy extra paint?
Yes. Always buy 10–15% more than calculated for touch-ups, mistakes, and future repairs. Keep leftover paint sealed for color-matched touch-ups later.
Does surface texture affect coverage?
Yes. Smooth drywall gets the best coverage. Textured walls, stucco, brick, and rough wood can reduce coverage by 20–50%, requiring more paint per square foot.
How do I convert gallons to liters?
1 US gallon = 3.785 liters. The calculator shows both units automatically so you can purchase in either measurement system.
Can I use this for exterior projects?
Yes. Select "Exterior Paint" for the correct coverage rate (300 ft²/gal). Enter the wall dimensions of your house exterior, deducting doors and windows as usual.