Paint Calculator
Estimate gallons of paint for interior walls, ceilings, and exterior surfaces — with coat and waste adjustments.
Your Paint Estimate
- Measure walls — add up all wall lengths for "total wall length." Use wall height for width.
- Select paint type — standard latex covers 350 ft²/gal. Premium paints cover more per coat.
- Account for coats — multiply your gallon result by 2 for two coats. Dark-to-light changes may need 3 coats.
- Deduct openings — subtract ~20 ft² per door and ~15 ft² per window from your total.
- Buy extra — always buy one extra gallon for cutting in, touch-ups, and future repairs.
How Much Paint Do I Need?
A gallon of standard latex paint covers approximately 350 square feet on smooth drywall with one coat. Most paint jobs require two coats for proper coverage and color consistency — so that same gallon effectively covers about 175 square feet finished. A typical 12 × 12 ft room with 8-foot ceilings has roughly 384 square feet of wall area (minus doors and windows), needing about 2 gallons for two coats.
Coverage drops significantly on textured surfaces, unpainted drywall, bare wood, and when making dramatic color changes (especially light over dark). In these cases, apply a tinted primer first — it improves coverage and reduces the number of topcoats needed.
Paint Coverage by Surface Type
Coverage varies dramatically based on the surface being painted:
| Surface | Coverage per Gallon | Notes |
|---|---|---|
| Smooth drywall (painted) | 350–400 ft² | Best case — previously painted smooth walls |
| New/unpainted drywall | 250–300 ft² | Porous — absorbs paint. Prime first. |
| Textured drywall | 200–300 ft² | Knockdown and orange peel reduce coverage |
| Wood trim/doors | 300–350 ft² | Smoother than walls but often brushed, not rolled |
| Exterior stucco | 150–250 ft² | Very porous — may need 2 coats of primer |
| Brick/masonry | 100–150 ft² | Extremely porous — prime first, expect 3 total coats |
These are per-coat figures. Always plan for two coats minimum. Dark-to-light color changes, bright reds, and deep blues may need 3–4 coats even with primer.
Gallons by Room Size (2 coats, standard paint)
| Room | Wall Area | Gallons (2 coats) | Approximate Cost |
|---|---|---|---|
| Bathroom (6×8 ft) | 168 ft² | 1 gallon | $30–$60 |
| Bedroom (10×12 ft) | 352 ft² | 2 gallons | $60–$120 |
| Living room (14×18 ft) | 512 ft² | 3 gallons | $90–$180 |
| Open plan (20×30 ft) | 800 ft² | 5 gallons | $150–$300 |
| Whole house interior | ~2,500 ft² | 15 gallons | $450–$900 |
Assumes 8-ft ceilings, 2 coats, 350 ft²/gal coverage. Deduct ~20 ft² per door, ~15 ft² per window.
Coverage per Gallon by Paint Finish
| Finish | Sq Ft per Gallon | Best For | Coats Typically Needed |
|---|---|---|---|
| Flat / Matte | 350–400 ft² | Ceilings, low-traffic walls | 2 |
| Eggshell | 300–350 ft² | Living rooms, bedrooms | 2 |
| Satin | 300–350 ft² | Kitchens, bathrooms, hallways | 2 |
| Semi-Gloss | 250–300 ft² | Trim, doors, cabinets | 2–3 |
| Gloss / High-Gloss | 200–250 ft² | Furniture, accent trim | 3 |
| Primer | 200–300 ft² | New drywall, color changes | 1 |
Higher sheen = lower coverage per gallon. Darker colors and new drywall often need an extra coat. Always check the label — premium paints can cover more.
Formulas
Area-based coverage calculation:
With waste = Wall area × (1 + Waste %)
Gallons per coat = Total area ÷ Coverage rate
Total gallons = Gallons per coat × Number of coats
This calculator gives a single-coat estimate. Multiply by 2 for standard two-coat coverage.
Related Calculators
Measure your wall or ceiling area first for accurate paint quantities. Browse the surface calculator collection.
Frequently Asked Questions
How many gallons of paint for a 12×12 room?
A 12×12 ft room with 8-foot ceilings has about 384 ft² of wall area (before deducting windows and doors). After deductions, roughly 320–340 ft². For two coats with standard latex paint (350 ft²/gal), you need about 2 gallons. Buy an extra quart for cutting in and touch-ups.
Do I need primer before painting?
Primer is required for bare drywall, raw wood, and major color changes (dark to light). It seals porous surfaces and improves paint adhesion. On previously painted surfaces in good condition with a similar color change, a paint-and-primer-in-one product or self-priming paint may be sufficient. Skip primer on bare surfaces and you will use more paint and get a less even finish.
How many gallons of paint do I need for a room?
A standard 12×12 ft room with 8-foot ceilings has roughly 350 ft² of wall area (accounting for a door and window). One gallon covers 350–400 ft², so one gallon per coat is typical for this size. For two coats, buy 2 gallons. Use the calculator above for exact quantities — enter each wall separately for irregular rooms.
What is the difference between paint finishes?
Flat/matte hides imperfections best but is hard to clean — good for ceilings and low-traffic walls. Eggshell and satin are the most popular for walls — slightly reflective and washable. Semi-gloss is used for trim, doors, and bathrooms because it is moisture-resistant and easy to wipe down. Gloss is highly durable and used for doors, cabinets, and furniture but highlights surface flaws.
How do I account for windows and doors?
Subtract the area of large openings (windows, doors, garages) from the total wall area for a tighter estimate. If you don't want to measure every opening, use a small waste factor instead and buy an extra quart for touch-ups.