Paint Needed
0 gal
Primer Needed
0 gal
Total Cost
$0.00
| Item | Amount |
|---|---|
| Wall Area | 0 sq ft |
| Ceiling Area | 0 sq ft |
| Doors & Windows | 0 sq ft |
| Total Paintable | 0 sq ft |
| Coats | 2 |
| Paint Gallons | 0 gal |
| Primer Gallons | 0 gal |
| Total Cost | $0.00 |
Room Paint Calculator: How Much Paint Do You Really Need in 2025?
Stop guessing and start painting with confidence. Our room paint calculator uses professional formulas to tell you exactly how many gallons of paint and primer you need — down to the last drop.
How the Room Paint Calculator Works
We calculate total surface area using:
- Walls: 2 × (Length × Height) + 2 × (Width × Height)
- Ceiling: Length × Width (optional)
- Subtract: Doors (21 sq ft each), Windows (15 sq ft each)
- Coverage: 350–400 sq ft per gallon (average)
- Coats: Multiply by 1, 2, or 3
- Primer: 1 coat, 300 sq ft/gal
Example Calculation
12 ft × 10 ft × 8 ft room, 1 door, 2 windows, 2 coats, ceiling included:
- Walls: 2×(12×8) + 2×(10×8) = 352 sq ft
- Ceiling: 12×10 = 120 sq ft
- Subtract: 1×21 + 2×15 = 51 sq ft
- Total: 421 sq ft
- 2 Coats: 842 sq ft → 2.4 gallons (buy 3)
- Primer: 421 sq ft → 1.4 gallons (buy 2)
Paint Coverage Guide (per Gallon)
| Surface | Coverage (sq ft) | Notes |
|---|---|---|
| Smooth drywall | 350–400 | New or previously painted |
| Textured walls | 250–300 | Use roller with thick nap |
| Ceiling | 300–350 | Flat paint recommended |
| Wood trim | 300–400 | Semi-gloss or satin |
| Brick | 200–250 | Needs primer |
Paint Types & When to Use Them
- Flat: Ceilings, low-traffic areas
- Eggshell: Living rooms, bedrooms
- Satin: Kitchens, bathrooms
- Semi-gloss: Trim, doors, high-moisture
- High-gloss: Furniture, accents
Primer: When You Need It
Always prime:
- New drywall
- Bare wood
- Dark to light color change
- Stains or water damage
- Switching from oil to latex
Cost Breakdown Example
| Item | Qty | Price | Total |
|---|---|---|---|
| Paint (3 gal) | 3 | $35 | $105 |
| Primer (2 gal) | 2 | $25 | $50 |
| Brushes & Rollers | — | — | $30 |
| Tape & Drop Cloth | — | — | $20 |
| Total | — | — | $205 |
Pro Tips for Perfect Results
- Buy 10% extra for touch-ups
- Stir, don’t shake — avoids bubbles
- Cut in first, then roll
- Use a ⅜" nap roller for smooth walls
- Paint in 3×3 sections to avoid lap marks
- Wait 2–4 hours between coats
- Clean tools with warm soapy water (latex)
Common Mistakes to Avoid
- Skipping primer on new drywall
- Painting in direct sunlight
- Using cheap brushes (leaves streaks)
- Not sanding between coats
- Overloading the roller
Tools You’ll Need
- 9" roller with extension pole
- 2" angled brush for cutting in
- Paint tray and liners
- Drop cloths
- Blue painter’s tape
- Putty knife
- Sandpaper (120–220 grit)
Environmental & Safety Tips
- Use low-VOC or zero-VOC paint
- Open windows for ventilation
- Wear a mask when sanding
- Store paint in a cool, dry place
- Dispose of rags safely (fire hazard)
Related Calculators
After painting, try:
FAQs
How many gallons for a 12x12 room? About 2 gallons (2 coats, no ceiling).
Can I mix paint brands? Only if same type and sheen.
How long does paint last? Unopened: 10 years. Opened: 2 years.
Should I paint ceiling white? Yes — reflects light, makes room feel taller.
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