Paint Calculator
Calculate exact paint volume in gallons and liters required for your room, including wall area, ceiling coverage, and window subtractions.
Paint Required
How to Use This Paint Calculator
Estimating paint volume accurately prevents extra trips to the store while avoiding wasted paint cans. Use this tool with simple step-by-step room inputs:
- Room Dimensions: Enter length, width, and wall height in feet or meters.
- Doors & Windows: Enter counts for standard doors (21 sq ft / 2 m² subtracted) and windows (15 sq ft / 1.4 m² subtracted).
- Number of Coats: Standard interior walls require two full coats for uniform coverage and rich color depth.
- Include Ceiling: Check the box if you plan to paint the ceiling using the same paint formula.
Paint Calculation Formulas & Standards
Standard architectural paint coverage calculations rely on industry benchmarks for surface area and liquid volume:
Wall Surface Area Formula
Total perimeter multiplied by height minus door and window openings:
Wall Area = 2 x (Length + Width) x Height - Openings
Gallon & Liter Spreading Rate
Standard paint spreads at approximately 350 sq ft per gallon (9 sq meters per liter):
Gallons = (Total Area x Coats) / 350
Room Paint Coverage Quick Reference Table
Estimated paint quantities for typical residential rooms based on 8-foot ceiling heights and 2 coats of paint.
| Room Size | Dimensions | Wall Surface Area | Gallons (2 Coats) | Liters (2 Coats) |
|---|---|---|---|---|
| Small Bathroom | 6 x 8 ft | 180 sq ft | 1 Gallon | 3.8 Liters |
| Standard Bedroom | 12 x 12 ft | 330 sq ft | 2 Gallons | 7.5 Liters |
| Master Bedroom | 15 x 20 ft | 510 sq ft | 3 Gallons | 11.3 Liters |
| Large Living Room | 20 x 25 ft | 670 sq ft | 4 Gallons | 15.1 Liters |
Frequently Asked Questions
How many square feet does one gallon of paint cover?
One gallon of standard interior paint covers roughly 350 to 400 square feet on smooth, primed walls. Textured walls or unprimed drywall absorb more paint, reducing coverage closer to 250 to 300 square feet per gallon.
Do I need primer before painting interior walls?
Primer is recommended when painting bare drywall, making drastic color shifts (such as dark to light), or covering water stains. Paint-and-primer combinations work well for repainting previously painted walls of similar tones.
How do doors and windows affect paint volume?
A standard interior door accounts for approximately 21 square feet, while a standard window subtracts 15 square feet of non-painted wall space. Factoring in openings prevents buying unnecessary paint.
How much extra paint should I buy for touch ups?
Purchasing an extra 10 percent allowance or keeping one quart of leftover paint ensures exact color matches for future scratch repairs and wall patches.
