Paint Calculator
Calculate paint needed for rooms or exteriors. Accounts for doors, windows, coats, and primer with cost estimates.
Room Dimensions
Paint Needed
2 gallons
Paint Coverage Guide
- Standard: 350-400 sq ft/gal
- Premium: 400-450 sq ft/gal
- Rough surfaces: 250-300 sq ft/gal
- Same color: 1-2 coats
- Light over dark: 2-3 coats
- New drywall: primer + 2 coats
- Always buy slightly more paint than calculated - colors vary between batches
- Use primer on new drywall, stains, or when making drastic color changes
- Paint with a W pattern for even coverage
- Allow proper drying time between coats (2-4 hours for latex)
- Paint in good lighting to spot missed areas
Related Calculators
About This Calculator
How much paint do you actually need? The average DIYer either buys too much (wasting $50-100) or too little (requiring a frustrating mid-project trip to the store where colors might not match). This Paint Calculator gives you the exact number of gallons needed for walls, ceilings, and trim—accounting for doors, windows, multiple coats, and primer requirements.
The numbers that matter: One gallon of paint covers 350-400 square feet under ideal conditions. That means a standard 12×12 room with 8-foot ceilings needs about 2 gallons for two coats (after subtracting doors and windows). But real-world coverage varies dramatically based on surface texture, color changes, and application method.
2026 paint costs: Quality interior paint now ranges from $25-80 per gallon depending on brand. Sherwin-Williams Emerald runs $74-80/gallon, while Behr Premium from Home Depot costs $35-50/gallon. With the average room requiring 2 gallons plus primer, a single room paint project costs $75-250 in materials alone.
Why accurate calculation matters: Buy 10-15% extra for touch-ups and future repairs. Paint colors vary between batches, so having extra from the same batch ensures consistent touch-ups for years. This calculator factors in all the variables so you buy exactly what you need—no more, no less.
How to Use the Paint Calculator
- 1**Choose your input mode**: Enter room dimensions (length, width, height) or input direct wall area if you already measured.
- 2**Enter room dimensions**: Standard ceiling height is 8 feet. Measure length and width at the longest points.
- 3**Specify doors and windows**: Each standard door is ~20 sq ft, windows average 12-15 sq ft. These reduce paintable area.
- 4**Select number of coats**: Use 2 coats for most projects, 3 coats when covering dark colors with light.
- 5**Toggle primer if needed**: Required for new drywall, drastic color changes, or stain coverage.
- 6**Switch to Advanced mode**: Customize coverage rates based on your specific paint and surface texture.
- 7**Add ceiling and trim separately**: Ceilings typically use flat ceiling paint; trim uses semi-gloss or high-gloss.
- 8**Round up to whole gallons**: Paint is sold in quarts and gallons—buying quarts at $15-20 each is rarely cost-effective.
Formula
Gallons Needed = (Paintable Area × Number of Coats) ÷ Coverage per Gallon
Wall Area = Perimeter × Ceiling Height
Perimeter = 2 × (Length + Width)
Deductions = (Doors × 20 sq ft) + (Windows × 15 sq ft)
Paintable Area = Wall Area - DeductionsThe paint calculation starts with total wall area (room perimeter multiplied by ceiling height). Standard deductions are 20 square feet per door and 15 square feet per window. The remaining paintable area is multiplied by the number of coats (typically 2) and divided by coverage rate (typically 350 sq ft per gallon for standard paint, 250-300 for primer). Always round up to whole gallons and add 10-15% for touch-ups.
Paint Coverage Rates by Type (2026)
Standard Coverage Per Gallon:
| Paint Type | Coverage | Best For |
|---|---|---|
| Flat/Matte | 350-400 sq ft | Ceilings, low-traffic walls |
| Eggshell | 350-400 sq ft | Living rooms, bedrooms |
| Satin | 350-400 sq ft | High-traffic areas, trim |
| Semi-Gloss | 300-350 sq ft | Kitchens, bathrooms, trim |
| High-Gloss | 300-350 sq ft | Doors, cabinets, accent |
| Primer | 200-300 sq ft | New surfaces, stain block |
| Ceiling Paint | 350-400 sq ft | Ceilings (thicker formula) |
Real-World Coverage Adjustments:
| Surface Condition | Coverage Reduction |
|---|---|
| Smooth, primed | 0% (full coverage) |
| Light texture | -10% (315-360 sq ft) |
| Orange peel texture | -20% (280-320 sq ft) |
| Knockdown texture | -25% (262-300 sq ft) |
| Heavy texture/popcorn | -30% (245-280 sq ft) |
| New/unprimed drywall | -25% (use primer first) |
| Porous wood | -30% (prime first) |
Application Method Impact:
| Method | Efficiency | Notes |
|---|---|---|
| Brush only | 100% | Slowest, visible strokes |
| Roller | 95-100% | Best for walls/ceilings |
| HVLP spray | 75-85% | Faster, some overspray |
| Airless spray | 60-70% | Fastest, most waste |
Pro Tip: For spray applications, add 25-40% to your paint estimate to account for overspray.
2026 Paint Prices by Brand
Interior Paint Prices Per Gallon:
| Brand | Budget Line | Mid-Range | Premium |
|---|---|---|---|
| Behr (Home Depot) | $28-35 | $38-48 | $55-65 |
| Valspar (Lowe's) | $25-32 | $35-45 | $48-60 |
| Sherwin-Williams | $38-45 | $55-65 | $70-80 |
| Benjamin Moore | $45-55 | $60-70 | $75-85 |
| PPG | $35-42 | $48-58 | $62-72 |
Sherwin-Williams 2026 Interior Lineup:
| Product | Price/Gallon | Coverage | Features |
|---|---|---|---|
| Captivate | $38 | 350 sq ft | Budget option |
| Cashmere | $60 | 400 sq ft | Popular choice |
| SuperPaint | $65 | 400 sq ft | Air purifying |
| Duration | $70 | 400 sq ft | Washable |
| Emerald | $75 | 400+ sq ft | Premium coverage |
Behr 2026 Interior Lineup:
| Product | Price/Gallon | Coverage | Features |
|---|---|---|---|
| Ultra | $32 | 350 sq ft | Value option |
| Premium Plus | $38 | 400 sq ft | Paint + primer |
| Marquee | $52 | 400 sq ft | One-coat coverage |
| Dynasty | $58 | 400 sq ft | Stain-resistant |
Exterior Paint (Higher Durability Needed):
| Brand | Price Range | Lifespan |
|---|---|---|
| Behr Exterior | $35-55 | 5-7 years |
| Sherwin-Williams Exterior | $55-85 | 7-10 years |
| Benjamin Moore Exterior | $60-90 | 8-12 years |
| Rhino Shield (ceramic) | $80-120 | 25 years |
Cost Per Room (Average 12×12):
| Quality Level | 2 Gallons + Primer | Total |
|---|---|---|
| Budget | $64 + $30 | ~$95 |
| Mid-Range | $110 + $35 | ~$145 |
| Premium | $150 + $40 | ~$190 |
When and How to Use Primer
When Primer is REQUIRED:
| Situation | Primer Type | Why |
|---|---|---|
| New drywall | PVA primer | Seals porous surface |
| New joint compound | PVA primer | Different porosity than paper |
| Bare wood | Wood primer | Prevents tannin bleed |
| Bare metal | Metal primer | Prevents rust |
| Dark to light color | High-hide primer | Reduces coats needed |
| Water stains | Shellac primer | Blocks stain bleed-through |
| Smoke damage | Shellac/Kilz | Seals odor and stain |
| Oil-based to latex | Bonding primer | Adhesion between types |
| Glossy surfaces | Bonding primer | Deglossing alternative |
When You Can SKIP Primer:
- Repainting same or similar color
- Using high-quality paint-and-primer combo
- Surface already primed and in good condition
- Going from light to dark color (easier coverage)
Primer Coverage and Cost:
| Primer Type | Coverage | Price/Gallon | Best Use |
|---|---|---|---|
| PVA (Drywall) | 200-300 sq ft | $15-25 | New drywall |
| Latex All-Purpose | 250-350 sq ft | $25-35 | General use |
| Shellac (BIN) | 200-275 sq ft | $40-55 | Stain blocking |
| Bonding/Adhesion | 300-350 sq ft | $30-45 | Slick surfaces |
| Kilz Original | 200-300 sq ft | $25-35 | Odor sealing |
Two-Coat Primer Rule:
New drywall requires TWO primer coats for proper sealing. The first coat is absorbed; the second provides the actual sealing layer. Skipping the second coat results in uneven sheen and visible joint compound lines (called "flashing").
Room-by-Room Paint Calculations
Standard Room Calculation Formula:
Wall Area = Perimeter × Ceiling Height
Deductions = (Doors × 20 sq ft) + (Windows × 15 sq ft)
Paintable Area = Wall Area - Deductions
Gallons Needed = (Paintable Area × Coats) ÷ Coverage Rate
Common Room Sizes:
| Room | Dimensions | Wall Area | After Deductions | 2-Coat Gallons |
|---|---|---|---|---|
| Small bedroom | 10×10×8 | 320 sq ft | ~280 sq ft | 2 gallons |
| Master bedroom | 14×16×8 | 480 sq ft | ~400 sq ft | 2-3 gallons |
| Living room | 18×20×8 | 608 sq ft | ~530 sq ft | 3-4 gallons |
| Kitchen | 12×14×8 | 416 sq ft | ~340 sq ft | 2-3 gallons |
| Bathroom | 8×10×8 | 288 sq ft | ~250 sq ft | 1-2 gallons |
| Home office | 10×12×8 | 352 sq ft | ~300 sq ft | 2 gallons |
Ceiling Paint:
| Room Size | Ceiling Area | Gallons Needed |
|---|---|---|
| 10×10 | 100 sq ft | 1 gallon (2 coats) |
| 12×12 | 144 sq ft | 1 gallon (2 coats) |
| 14×16 | 224 sq ft | 1-2 gallons |
| 18×20 | 360 sq ft | 2 gallons |
Trim Paint (Semi-Gloss):
| Trim Type | Linear Feet | Square Feet | Notes |
|---|---|---|---|
| Baseboard (per room) | 40-60 ft | 20-30 sq ft | 4" baseboard |
| Crown molding (per room) | 40-60 ft | 15-20 sq ft | 3-4" crown |
| Door casing (each) | 17 ft | 8-10 sq ft | Both sides |
| Window casing (each) | 12 ft | 5-7 sq ft | Standard window |
| Single door (each) | - | 20-25 sq ft | Both sides |
Whole House Estimate (2,000 sq ft home):
| Area | Gallons | Paint Type |
|---|---|---|
| Walls | 12-15 | Eggshell/Satin |
| Ceilings | 5-7 | Flat ceiling |
| Trim/Doors | 3-4 | Semi-gloss |
| Primer | 8-10 | If needed |
| Total | 28-36 |
Paint Sheen Guide: Choosing the Right Finish
Sheen Comparison Chart:
| Sheen | Durability | Washability | Hides Imperfections | Best Rooms |
|---|---|---|---|---|
| Flat/Matte | Low | Poor | Excellent | Ceilings, formal rooms |
| Matte Enamel | Medium | Fair | Very Good | Bedrooms, dining |
| Eggshell | Medium | Good | Good | Living, bedrooms |
| Satin | Medium-High | Very Good | Fair | High-traffic, kids |
| Semi-Gloss | High | Excellent | Poor | Kitchen, bath, trim |
| High-Gloss | Very High | Excellent | Very Poor | Doors, cabinets |
Room-by-Room Recommendations:
| Room | Walls | Ceiling | Trim |
|---|---|---|---|
| Living Room | Eggshell | Flat | Satin/Semi-gloss |
| Bedroom | Flat/Eggshell | Flat | Satin |
| Kitchen | Satin/Semi-gloss | Flat/Satin | Semi-gloss |
| Bathroom | Satin/Semi-gloss | Satin | Semi-gloss |
| Kids Room | Satin | Flat | Semi-gloss |
| Hallway | Satin | Flat | Semi-gloss |
| Home Office | Eggshell | Flat | Satin |
| Basement | Satin | Flat | Semi-gloss |
Why Sheen Matters for Imperfections:
Higher sheen = more light reflection = more visible wall imperfections. If your walls have:
- Visible seams or tape lines → Use flat/matte
- Minor texture inconsistencies → Use eggshell
- Good drywall but some dings → Use satin
- Perfect smooth walls → Any sheen works
The Wet vs. Dry Look:
All sheens look glossier when wet. A satin paint that looks semi-gloss wet will dry to proper satin. Wait 24 hours before judging the final sheen. Some premium paints (Benjamin Moore Regal, Sherwin-Williams Emerald) have "truer" sheens that look consistent wet and dry.
DIY Painting Tips from the Pros
Surface Preparation (80% of the Work):
| Step | Time | Why It Matters |
|---|---|---|
| Clean walls | 15 min/room | Paint won't stick to dirt/grease |
| Patch holes | 30 min/room | Spackle, sand, feather edges |
| Sand glossy surfaces | 15 min/room | Create "tooth" for adhesion |
| Tape edges | 20 min/room | Clean lines, protect surfaces |
| Lay drop cloths | 10 min/room | Paint splatter is inevitable |
Professional Cutting-In Technique:
- Load brush 1/3 into paint
- Tap (don't wipe) excess on container edge
- Start 1" from edge, paint toward corner
- Feather out strokes away from edge
- Maintain wet edge to avoid lap marks
Roller Technique for Smooth Finish:
- Load roller in tray, roll off excess
- Apply in "W" pattern (3 ft wide)
- Fill in with straight vertical strokes
- Light pressure on final pass
- Overlap previous section while wet
Common DIY Mistakes:
| Mistake | Result | Prevention |
|---|---|---|
| Skipping primer | Uneven coverage, flashing | Always prime bare/repaired surfaces |
| Too thin coats | Visible old color | Apply at proper coverage rate |
| Too thick coats | Drips, extended dry time | Multiple thin coats > one thick |
| Painting too fast | Lap marks, roller lines | Maintain wet edge, work in sections |
| Wrong temperature | Poor adhesion, bubbling | Paint at 50-85°F, <85% humidity |
| Removing tape late | Peeling paint | Remove while last coat is tacky |
Dry Time Between Coats:
| Paint Type | Touch Dry | Recoat Time |
|---|---|---|
| Latex/Acrylic | 1-2 hours | 2-4 hours |
| Alkyd/Oil | 6-8 hours | 24 hours |
| Primer | 30-60 min | 1-3 hours |
| High humidity | 2x normal | 2x normal |
Special Situations and Problem Solving
Painting Over Problem Surfaces:
| Problem | Solution | Product Recommendation |
|---|---|---|
| Water stains | Shellac primer | Zinsser BIN, Kilz Original |
| Smoke/nicotine | Shellac primer (2 coats) | Zinsser BIN |
| Mold/mildew | Clean, treat, mold primer | Zinsser Mold Killing Primer |
| Crayon/marker | Shellac primer | Zinsser BIN |
| Pet odor | Shellac primer, odor sealer | Kilz Original |
| Grease stains | Degrease, shellac primer | TSP cleaner, then BIN |
| Bleeding wood tannins | Shellac primer | Zinsser BIN, Cover Stain |
Drastic Color Changes:
| From → To | Extra Steps | Coats Needed |
|---|---|---|
| Dark → Light | Gray-tinted primer | 2-3 coats |
| Red → White | Gray primer | 3+ coats |
| Black → White | Gray primer | 3+ coats |
| Light → Dark | No primer needed | 2 coats |
| Any → Same | No primer | 2 coats |
Exterior Painting Considerations:
| Factor | Requirement |
|---|---|
| Temperature | 50-85°F during application AND drying |
| Humidity | Below 85% relative humidity |
| Rain | No rain 24-48 hours after painting |
| Sun | Avoid direct sun on surface while painting |
| Wind | Low wind prevents debris and fast drying |
| Dew point | Paint when surface temp is 5°F above dew point |
When NOT to Paint:
- Temperature below 50°F or above 90°F
- Rain expected within 24 hours (exterior)
- Humidity above 85%
- Direct sunlight on the surface (causes bubbling)
- Surface is dirty, dusty, or wet
- Lead paint present without proper containment (pre-1978 homes)
Pro Tips
- 💡Always buy 10-15% extra paint for touch-ups—color batches vary slightly and stores can't perfectly match later.
- 💡Test paint colors on actual walls with sample pots or peel-and-stick samples—colors look different in your lighting.
- 💡Calculate ceiling and walls separately—use flat ceiling paint for ceilings, eggshell or satin for walls.
- 💡Prime all patched areas, even small nail holes—bare spackle shows through as "flashing" with different sheen.
- 💡Remove painter's tape while the final coat is still slightly tacky—waiting until fully dry can peel the paint.
- 💡Use a 1/2" nap roller for smooth walls, 3/4" for light texture, and 1" for heavy texture like knockdown.
- 💡Cut in corners and edges first, then roll walls while the cut-in paint is still wet to blend seamlessly.
- 💡Work from top to bottom: ceiling first, then walls, then trim last with semi-gloss.
- 💡In low light or evening, angle a work light across the wall to reveal missed spots and roller marks.
- 💡Store leftover paint upside-down (after sealing) to create an airtight seal that preserves it for years.
- 💡For exterior, schedule painting during cool mornings—avoid direct sunlight on the surface being painted.
- 💡Use conditioner (Floetrol for latex, Penetrol for oil) in hot weather to extend working time and improve flow.
Frequently Asked Questions
A 12×12 room with 8-foot ceilings has approximately 384 sq ft of wall area. After subtracting 2 doors (~40 sq ft) and 2 windows (~30 sq ft), you have ~314 sq ft of paintable wall. At 350 sq ft per gallon, that's about 1 gallon per coat. For the recommended 2 coats, you need 2 gallons of wall paint. Add 1 gallon for the 144 sq ft ceiling (2 coats). Buy an extra quart for touch-ups.
