Paint Calculator (Gallons & Liters Needed per Room)
Estimate paint volume in gallons and liters based on room dimensions, doors, windows, and coats.
TL;DR: Paint Calculator determines paint requirements for interior and exterior walls, deducting window/door openings and computing total gallons or liters needed across multiple coats.
How Many Gallons of Paint Do I Need for a Room?
Paint needed is calculated by: Net Wall Area (sq ft) × Number of Coats / Paint Coverage (typically 350 to 400 sq ft per gallon). For example, a 12 ft × 15 ft room with 8 ft ceilings has 432 sq ft gross wall area; subtracting doors/windows leaves ~380 sq ft. Two coats require ~2 gallons of paint.
How to Use the Paint Calculator
Our Paint Calculator performs high-precision mathematical operations directly in your browser with zero latency and complete client-side privacy.
- Enter the room's length, width, and ceiling height.
- Enter the number of standard doors (21 sq ft each) and windows (15 sq ft each) to deduct.
- Select the number of paint coats desired (1, 2, or 3 coats).
- Specify paint coverage rate (default standard is 350 sq ft / 32.5 m² per gallon).
- Review the total paint required in gallons, quarts, and liters for trim, ceiling, and walls.
Mathematical Formula & Equations
Estimates paint gallons required for interior rooms and exterior walls accounting for two-coat coverage.
Calculation Example
A 12x14 ft room with 8 ft ceilings (416 sq ft wall area) minus 40 sq ft for door and window = 376 sq ft. For 2 coats (752 sq ft total): Need $752 / 350 = 2.15 \implies 3\text{ Gallons}$.
100% Client-Side Privacy & Data Security
All calculations, amortization schedules, variables, and sensitive numerical datasets execute 100% locally in your web browser memory. Your financial, medical, and personal values are never transmitted, logged, or uploaded to any external server.
Frequently Asked Questions
- One standard gallon of interior wall paint covers approximately 350 to 400 square feet with a single coat on smooth primed drywall.
- A 12x12 room with 8 ft ceilings has 384 sq ft of gross wall area. After deducting 1 door and 2 windows (~51 sq ft), net area is ~333 sq ft. Two coats require approximately 2 gallons of paint.
- Two coats are strongly recommended for durability, uniform sheen, and proper color saturation, especially when covering dark existing colors or unprimed surfaces.
- Ceiling area equals `Room Length × Room Width`. A 12x15 room has a 180 sq ft ceiling, which requires approximately 0.5 to 1 gallon for two coats.
- One US liquid gallon equals approximately 3.785 liters (1 liter covers ~10 square meters).
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