Paint Calculator - How Much Paint Do I Need?
Calculate exactly how many gallons of paint you need for any room. Account for doors, windows, number of coats, and paint type.
Paint Options
Quick Answer
1 gallon of paint covers 350-400 square feet per coat. A typical 12×12 room needs 1.5-2 gallons for two coats (after subtracting doors and windows).
Whether you're refreshing a single room or tackling a whole-house painting project, knowing exactly how much paint to buy saves you money and extra trips to the store. Our paint calculator considers room dimensions, doors, windows, ceiling options, paint type, and number of coats to give you accurate estimates.
Dr. Snezana Lawrence
Mathematical Historian
15+ years experience
PhD from Yale University. Published mathematical historian ensuring precision in all calculations.
Education
PhD in Mathematical History - Yale University
How to Calculate Paint Needed
Calculate Wall Perimeter
Add length + width + length + width to get the room perimeter.
Multiply by Height
Perimeter × ceiling height = total wall area in square feet.
Subtract Openings
Subtract doors (21 sq ft each) and windows (15 sq ft each).
Multiply by Coats
Net area × number of coats = total coverage needed.
Divide by Coverage Rate
Total coverage ÷ 400 sq ft/gallon = gallons needed.
Formula: Gallons = (Perimeter × Height - Openings) × Coats ÷ Coverage Rate
Paint Coverage Chart
| Paint Type | Coverage (sq ft/gal) | Best For |
|---|---|---|
| Interior Latex (Flat) | 400-450 | Walls, ceilings, low-traffic areas |
| Interior Latex (Eggshell) | 350-400 | Living rooms, bedrooms, dining rooms |
| Interior Latex (Satin) | 350-400 | Kitchens, bathrooms, hallways |
| Semi-Gloss | 350-400 | Trim, doors, cabinets, high-moisture areas |
| High-Gloss | 300-350 | Trim, furniture, accent pieces |
| Exterior Latex | 300-400 | Exterior walls, siding |
| Textured Paint | 250-300 | Hiding imperfections, ceilings |
| Primer | 400-500 | New drywall, stain blocking, color change |
Room Size Reference Chart
| Room | Dimensions | Wall Area* | Paint (2 coats) |
|---|---|---|---|
| Small Bedroom | 10×10' | 280 sq ft | 1.5 gal |
| Average Bedroom | 12×12' | 330 sq ft | 1.5-2 gal |
| Master Bedroom | 14×16' | 420 sq ft | 2-2.5 gal |
| Living Room | 15×20' | 490 sq ft | 2.5-3 gal |
| Kitchen | 12×14' | 360 sq ft | 2 gal |
| Bathroom | 8×10' | 250 sq ft | 1-1.5 gal |
| Garage (2-car) | 20×24' | 616 sq ft | 3-4 gal |
*Assumes 8-foot ceilings with 1 door and 2 windows subtracted
Pro Tips
Buy Extra for Touch-Ups
Purchase 10-15% more paint than calculated. You'll need it for touch-ups and future repairs. Paint colors can vary slightly between batches.
Use a Tinted Primer
When making dramatic color changes (dark to light or light to dark), use a primer tinted to match your topcoat. This reduces the number of finish coats needed.
Calculate Trim Separately
Doors, baseboards, and window trim typically use a different finish (semi-gloss). Budget about 1 quart per door and 1 quart per 100 linear feet of baseboard.
Account for Surface Texture
Textured walls, brick, or stucco absorb more paint. Reduce your expected coverage by 15-25% for these surfaces.
Check the Weather
For exterior painting, ideal conditions are 50-85°F with low humidity. Paint in direct sunlight can dry too fast, causing brush marks and poor adhesion.
Frequently Asked Questions
How much paint do I need for a 12×12 room?
A 12×12 room with 8-foot ceilings has approximately 330 square feet of wall space (after subtracting doors and windows). For two coats, you'll need about 1.5-2 gallons of wall paint.
How many square feet does 1 gallon of paint cover?
One gallon of standard interior latex paint covers approximately 350-400 square feet per coat on smooth surfaces. Textured surfaces reduce coverage to about 300 sq ft per gallon.
Should I buy more paint than calculated?
Yes, it's recommended to buy 10-15% more paint than calculated to account for touch-ups, spills, and variations in surface absorption. Our calculator rounds up to the nearest half-gallon for this reason.
How do I calculate paint for a ceiling?
Ceiling paint calculation is straightforward: multiply length × width to get square feet. For example, a 12×14 room has a 168 sq ft ceiling. Ceilings typically need one coat of ceiling paint.
Does paint color affect coverage?
Yes, darker colors may require additional coats for full coverage, especially when covering a lighter color. Red, yellow, and bright colors often need 3+ coats. Using a tinted primer helps reduce the number of topcoats needed.
How much paint do I need for trim and doors?
A standard interior door requires about 1/2 quart (for both sides). Window trim averages 1/4 quart per window. Baseboards typically need 1 quart per 100 linear feet.
Is primer included in paint coverage calculations?
Our calculator treats primer as a separate option. If using paint-and-primer-in-one, use the standard coverage rate. For bare surfaces, calculate primer and topcoat separately as they have different coverage rates.
How much does professional painting cost?
Professional interior painting typically costs $2-6 per square foot of wall space, including labor and materials. A 12×12 room averages $300-800 for professional painting. DIY saves 50-70% of this cost.
Dr. Snezana Lawrence
Mathematical Historian | PhD from Yale
Dr. Lawrence is a published mathematical historian with a PhD from Yale University. She ensures mathematical precision and accuracy in all our calculations, conversions, and academic score calculators. Her expertise spans computational mathematics and educational assessment.
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