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Free Paint Calculator
Paint Calculator: Know Exactly How Much Paint to Buy
Enter your room dimensions into the paint calculator above and instantly see how many gallons you need, whether primer is required, and what the project will cost in 2026.
How Much Paint for Common Rooms (2 Coats)
| 10x10 bedroom | 2 gallons + 1 primer |
| 12x12 bedroom | 2 gallons + 1 primer |
| 20x15 living room | 4 gallons + 2 primer |
| 2,000 sq ft home exterior | 15-20 gallons |
Paint Reference Guide
Paint Costs in 2026 (per Gallon)
| Budget interior paint | $25 - $40 |
| Premium interior paint (Behr, Sherwin-Williams) | $45 - $75 |
| Exterior paint | $35 - $65 |
| Primer | $20 - $35 |
Prices are 2026 US averages. Actual costs vary by region and supplier.
Recommended Depths for Paint
| Project / Use Case | Recommended Depth |
|---|---|
| Smooth walls (new drywall) | 350-400 sq ft per gallon |
| Lightly textured walls | 250-300 sq ft per gallon |
| Rough surfaces (stucco, brick) | 200-250 sq ft per gallon |
| Previously painted (same color) | 400 sq ft per gallon |
How to Calculate Paint Volume
Most landscaping suppliers sell paint by the cubic yard. To convert your project area to cubic yards, use this formula:
Our calculator also multiplies your cubic yard result by 0 tons/yd³ (the standard density for paint) to show estimated weight — essential if you are hauling the material yourself or need delivery pricing.
Paint Calculator: Coverage Rates, Primer Rules, and Brand Differences
A paint calculator estimates gallons by dividing your total wall area by the coverage rate of your paint. The standard formula is: (2 x (Length + Width) x Wall Height) / Coverage per Gallon x Number of Coats. For a 12x12 room with 8-foot ceilings, that is 384 square feet of wall. At 350 sq ft per gallon, one coat needs 1.1 gallons.
Coverage rates are not universal. They depend on surface texture and paint quality. Smooth new drywall accepts 350 to 400 sq ft per gallon. Lightly textured walls (orange peel, knockdown) absorb more paint and yield 250 to 300 sq ft per gallon. Rough exterior surfaces like stucco or brick drop to 200 to 250. Always check the can label: manufacturers print the rated coverage, and premium paints consistently outperform budget lines.
Primer deserves its own calculation because it follows different rules. One gallon of primer covers roughly 300 sq ft. You need primer on new drywall (it seals the porous paper facing), bare wood, water stains, and any drastic color change. Our calculator includes a primer toggle: when enabled, it adds primer gallons at 300 sq ft per gallon with no waste factor, since primer goes on in a single sealing coat.
Brand coverage differences are real and measurable. In independent testing, Behr Marquee consistently achieves advertised one-coat coverage near 400 sq ft per gallon on smooth walls. Sherwin-Williams Duration and Emerald lines rate around 350 to 400 with superior hide on color changes. Benjamin Moore Regal Select performs similarly at 400 sq ft per gallon but at a higher price point. Budget contractor-grade paints may claim 400 but deliver closer to 300 in practice. When comparing prices, divide cost per gallon by actual coverage to find the true cost per square foot.
Do not forget the ceiling and trim if your project includes them. Ceilings use flat paint at the same coverage rate as walls: a 12x12 ceiling needs about 0.4 gallons per coat. Trim and doors use semi-gloss enamel, which covers roughly 400 sq ft per gallon because it levels smoothly. For a whole-room project, calculate walls, ceiling, and trim separately, then round each up to the nearest quart.
Pro Tips & Insights
1
Always buy all your paint at once. Color can vary slightly between batches, and running out mid-project risks a visible mismatch on the final wall.
2
Primer is not optional on new drywall, bare wood, or drastic color changes. Skipping primer on these surfaces typically forces a third coat, which costs more than the primer would have.
3
A 9-inch roller covers walls roughly twice as fast as a brush. Use a brush only for cutting in edges and corners, then roll the large areas.
4
Paint stores will tint primer toward your topcoat color for free. Tinted primer dramatically improves coverage when painting over dark colors.
Frequently Asked Questions
How much paint do I need for a 12x12 room?▼
A 12x12 room with 8-foot ceilings has 384 square feet of wall space. At 350 sq ft per gallon on smooth walls, you need 1.1 gallons per coat, so buy 2 gallons for two coats. Our paint calculator above handles the exact math for your room dimensions.
Do I need primer before painting?▼
You need primer on new drywall, bare wood, stained surfaces, and when making drastic color changes (dark to light). You can skip primer when repainting a previously painted wall in a similar color with quality paint. When in doubt, prime: a $25 gallon of primer is cheaper than an extra $60 coat of finish paint.
How much does a gallon of paint cover?▼
One gallon covers 350 to 400 sq ft on smooth walls with one coat. Textured walls drop coverage to 250 to 300 sq ft per gallon. Brand matters: Behr Marquee advertises one-coat coverage at 400 sq ft per gallon, Sherwin-Williams Duration covers about 350, and Benjamin Moore Regal Select lands around 400 on smooth surfaces.
How much does it cost to paint a room in 2026?▼
DIY painting a 12x12 bedroom costs $80 to $200 in 2026: 2 gallons of quality paint ($50-$140), plus primer, tape, and rollers. Hiring a professional for the same room runs $300 to $800 depending on your market. An average home exterior costs $3,000 to $7,000 professionally painted.
How many coats of paint do I need?▼
Two coats is the standard for professional results. One coat suffices only when using premium one-coat products (like Behr Marquee) over a similar existing color. New drywall always needs primer plus two finish coats. Dark-to-light color changes need primer plus two coats minimum.