**Paint coverage formula**: **Total Paint Needed (gallons) = (Total Surface Area ÷ Coverage per Gallon) × Number of Coats**. **Standard coverage rates (2025)**: **1 gallon of paint covers**: **350-400 sq ft** for smooth walls (drywall, plaster). **250-350 sq ft** for textured/rough surfaces (popcorn ceiling, stucco, brick). **200-300 sq ft** for very porous surfaces (bare wood, unpainted drywall). **Primer**: 200-300 sq ft per gallon (lower coverage than paint). **Step-by-step paint calculation (example room)**: **Room dimensions**: 12 ft × 15 ft room, 8 ft ceilings. **Step 1: Calculate wall surface area**: Perimeter: (12 + 15) × 2 = **54 ft**.

Wall area: 54 ft × 8 ft = **432 sq ft**. **Step 2: Subtract doors and windows**: Standard door: 21 sq ft (3 ft × 7 ft).

Window: 15 sq ft each (assume 2 windows = 30 sq ft). **Total deductions**: 21 + 30 = **51 sq ft**. **Net wall area**: 432 - 51 = **381 sq ft**. **Step 3: Add ceiling (if painting)**: Ceiling area: 12 ft × 15 ft = **180 sq ft**. **Total paintable area**: 381 (walls) + 180 (ceiling) = **561 sq ft**. **Step 4: Calculate paint needed (2 coats)**: Coverage per gallon: 350 sq ft (smooth walls).

Paint for 1 coat: 561 ÷ 350 = **1.6 gallons**.

Paint for 2 coats: 1.6 × 2 = **3.2 gallons**. **Round up**: Buy **4 gallons** (includes 25% waste/touch-ups). **If using primer**: Primer coverage: 300 sq ft/gallon.

Primer needed: 561 ÷ 300 = **1.9 gallons** → Buy **2 gallons primer**. **Paint needed by room size (2 coats, 8 ft ceilings, walls + ceiling)**: **Small bathroom** (5×8 ft): 0.75 gallons. **Medium bedroom** (10×12 ft): 2 gallons. **Large bedroom** (12×15 ft): 3 gallons. **Living room** (15×20 ft): 4 gallons. **Open concept** (20×30 ft): 7 gallons. **How surface texture affects coverage**: **Smooth drywall** (new construction): **400 sq ft/gallon** (best coverage).

Use flat/eggshell paint for maximum spread. **Orange peel texture** (common): **350 sq ft/gallon** (standard coverage).

Most paint cans list this rate. **Knockdown texture**: **300 sq ft/gallon** (moderate).

Textured surface absorbs more paint. **Popcorn ceiling**: **250 sq ft/gallon** (heavy absorption).

Often need 3 coats.

Consider spray application (better coverage). **Brick/stucco**: **200 sq ft/gallon** (very porous).

First coat = primer/sealer (200 sq ft), subsequent coats 250-300 sq ft. **Bare wood** (unpainted): **250 sq ft/gallon** for primer. 300-350 sq ft for paint coats (wood grain drinks paint). **Coverage by paint sheen (affects spread)**: **Flat/matte**: **400-450 sq ft/gallon** (thinnest, best coverage). **Eggshell**: **350-400 sq ft/gallon** (standard). **Satin**: **350-400 sq ft/gallon**. **Semi-gloss**: **350-375 sq ft/gallon** (thicker, less coverage). **High-gloss**: **300-350 sq ft/gallon** (thickest, lowest coverage). **Number of coats needed**: **2 coats** = standard for most projects (hiding previous color, even finish). **1 coat** sufficient if: Repainting same color (touch-up).

Using high-quality paint with excellent hiding (Behr Marquee, Sherwin-Williams Duration).

Light to light color (white → beige). **3 coats** needed for: Dark to light color change (navy → white).

Bright/bold colors (red, yellow, orange require extra coats for even color).

Covering stains (water damage, smoke).

Painting over wallpaper (if not removing). **Cost estimation (2025 paint prices)**: **Budget paint** (Behr, Glidden): $25-$35/gallon. **Mid-range** (Benjamin Moore Regal, Sherwin-Williams ProMar): $40-$60/gallon. **Premium** (Benjamin Moore Aura, Sherwin-Williams Emerald): $65-$90/gallon. **Designer** (Farrow & Ball, Fine Paints of Europe): $100-$120/gallon. **Example project cost (12×15 ft bedroom)**: 4 gallons premium paint @ $70 = $280. 2 gallons primer @ $30 = $60.

Supplies (brushes, rollers, tape, drop cloths): $50. **Total DIY cost**: **$390**. **Professional labor**: $300-$600 additional ($2-$4/sq ft). **Total professional**: $690-$990. **Common mistakes that waste paint**: **Not accounting for texture** - Smooth wall formula (400 sq ft/gal) used on textured walls = run out mid-project. **Forgetting primer** - Bare drywall/dramatic color change needs primer (not included in paint calculation). **Overbuying** - Painting white → white with premium paint = 1 coat sufficient, don't buy 2x. **Underbuying** - Not adding 10-15% waste factor = need emergency paint run (color batch mismatch risk). **Mixing paint types** - Buying 3 gallons different sheens (flat + eggshell) = inconsistent finish. **Tips to minimize paint waste**: **Buy 5-gallon buckets** if need >4 gallons (cheaper, color consistency). **Save extra paint** in sealed container for touch-ups (lasts 2-5 years). **Use paint calculator apps** (Sherwin-Williams ColorSnap, Benjamin Moore paint calculator). **Measure twice** - Recalculate before buying. **Test coverage** - Paint one wall, measure actual coverage (may be better/worse than 350 sq ft estimate).

**Ceiling paint calculation**: **Formula**: Ceiling Area (sq ft) ÷ Coverage Rate × Number of Coats. **Ceiling coverage rates**: **Flat ceiling (smooth)**: 400 sq ft/gallon. **Textured ceiling (orange peel)**: 350 sq ft/gallon. **Popcorn ceiling**: **200-250 sq ft/gallon** (very absorbent, often spray applied). **Example**: 15×20 ft living room ceiling.

Area: 15 × 20 = **300 sq ft**.

Texture: Popcorn.

Coverage: 250 sq ft/gallon.

Coats: 2 (standard).

Calculation: (300 ÷ 250) × 2 = **2.4 gallons** → Buy **3 gallons ceiling white**. **Ceiling vs wall paint differences**: **Ceiling paint** is thicker (less dripping), flat sheen (hides imperfections), cheaper ($25-$35/gal). **Wall paint** is thinner, various sheens, more expensive ($35-$70/gal).

Don't use wall paint on ceiling (drips, waste).

Can use ceiling paint on walls if budget tight (but less durable). **Trim and door paint calculation (oil-based or semi-gloss latex)**: **Coverage rates for trim**: **Smooth wood trim** (primed): 400-450 sq ft/gallon. **Bare wood trim** (unpainted): 200-250 sq ft/gallon for primer, 350 sq ft for paint. **Trim linear foot formula**: **Baseboard**: 1 sq ft per linear foot (6-8 inch tall baseboards). **Crown molding**: 0.5-0.75 sq ft per linear foot. **Door/window casing**: 1.5 sq ft per opening (both sides). **Doors**: 20-25 sq ft per door (both sides). **Example trim calculation**: 12×15 ft bedroom. **Baseboard**: Perimeter 54 ft × 1 sq ft = 54 sq ft. **Door casing**: 2 doors × 1.5 sq ft = 3 sq ft. **Crown molding**: 54 ft × 0.75 sq ft = 40.5 sq ft. **Doors** (if painting): 2 × 22 sq ft = 44 sq ft. **Total trim area**: 54 + 3 + 40.5 + 44 = **141.5 sq ft**. **Paint needed** (semi-gloss, 2 coats): Coverage: 400 sq ft/gallon.

Calculation: (141.5 ÷ 400) × 2 = **0.71 gallons** → Buy **1 gallon trim paint**. **Typically 1 gallon trim paint covers 2-3 average bedrooms** (baseboards + doors). **Textured surface coverage (stucco, brick, concrete)**: **Exterior stucco**: **Primer/sealer**: 150-200 sq ft/gallon (first coat, fills pores). **Paint coats**: 200-300 sq ft/gallon (2 coats needed). **Example**: 1,500 sq ft stucco house.

Primer: 1,500 ÷ 175 = **8.6 gallons** → 9 gallons primer.

Paint: (1,500 ÷ 250) × 2 = **12 gallons** paint. **Brick**: **Unpainted brick**: 150-200 sq ft/gallon (very porous).

Prime with masonry sealer: 150 sq ft/gallon.

Paint: 200-250 sq ft/gallon, 2 coats. **Previously painted brick**: 300-350 sq ft/gallon (less absorption). **Concrete/cinder block**: **Floor**: 300-400 sq ft/gallon (epoxy or concrete paint). **Walls**: 200-300 sq ft/gallon (rough surface). **Wood siding**: **Smooth siding** (T1-11, shiplap): 350-400 sq ft/gallon. **Rough siding** (board and batten, cedar shingles): 250-300 sq ft/gallon (2 coats). **Primer on bare wood**: 250-300 sq ft/gallon. **Cabinet painting coverage**: **Kitchen cabinets** (20 linear feet): **Door fronts**: ~60 sq ft (both sides). **Face frames**: ~40 sq ft. **Total**: 100 sq ft. **Primer**: 100 ÷ 300 = 0.33 gallons. **Paint** (2 coats semi-gloss): (100 ÷ 350) × 2 = 0.57 gallons. **Total**: 1 quart primer + 1 quart paint (or 1 gallon for both if buying gallon sizes). **Bathroom/kitchen special coverage**: **High-humidity rooms** need: **2 coats primer** (mold/mildew resistant) = 200-250 sq ft/gallon. **2 coats semi-gloss/satin paint** (washable, moisture resistant) = 300-350 sq ft/gallon. **Example**: 8×10 ft bathroom (walls + ceiling, no windows).

Area: [(8+10)×2 × 8] + (8×10) = **368 sq ft**.

Primer (2 coats): (368 ÷ 250) × 2 = **2.9 gallons** → 3 gallons.

Paint (2 coats semi-gloss): (368 ÷ 325) × 2 = **2.3 gallons** → 3 gallons. **Multi-color room coverage**: **Accent wall + 3 walls**: Calculate each color separately. **Example**: 12×15 ft room, one 12-ft wall accent (red), other walls white. **Accent wall**: 12 ft × 8 ft = 96 sq ft.

Red paint (3 coats for bold color): (96 ÷ 350) × 3 = **0.82 gallons** → 1 gallon red. **Remaining walls**: [(15×2 + 12) × 8] - 96 = **240 sq ft**.

White paint (2 coats): (240 ÷ 375) × 2 = **1.3 gallons** → 2 gallons white. **Ceiling**: 12×15 = 180 sq ft.

White ceiling (2 coats): (180 ÷ 400) × 2 = **0.9 gallons** → included in 2 gallons white or buy separate gallon ceiling white ($28 vs $65 wall paint). **Paint calculator by project type (2025 quick reference)**: **Whole house interior** (2,000 sq ft, 8 ft ceilings, 15 rooms): Walls: 40-50 gallons.

Ceilings: 15-20 gallons.

Trim: 10-15 gallons. **Total**: 65-85 gallons ($2,500-$5,500 paint cost). **Exterior house** (2,000 sq ft siding): Primer: 15-20 gallons.

Paint: 30-40 gallons (2 coats).

Trim: 5-10 gallons. **Total**: 50-70 gallons ($1,500-$3,500 paint cost). **Single room repaint** (12×12 ft): Walls: 2 gallons.

Ceiling: 1 gallon.

Trim: 1 quart. **Total**: 3 gallons + 1 quart ($120-$250 paint cost). **Professional painter estimates** (they use tighter calculations): Pros calculate: Actual surface area - (doors + windows).

Add only 5-10% waste (vs DIY 15-25%).

Use contractor-grade paint (better coverage, 375-425 sq ft/gallon).

Result: Pro may use 20-30% less paint than DIY calculation. **Advanced tips**: **Spraying vs rolling**: Spraying uses 20-40% more paint (overspray waste).

Budget extra 1.5× gallons if spraying. **Color intensity**: Reds, oranges, yellows: Add 1 extra coat (pigment coverage issues).

Whites, neutrals: Standard 2 coats. **Sheen strategy**: Use flat on ceilings (best coverage, hides flaws).

Use eggshell/satin on walls (balanced coverage + durability).

Use semi-gloss on trim/doors (fewer coats needed, durable).