How to Calculate How Much Paint You Need
The formula is straightforward: measure the total wall area, subtract openings, then divide by coverage per gallon. Here's the exact math:
- Calculate wall area. Perimeter × ceiling height = total wall square footage. For a 14×12 room with 8-foot ceilings: (14 + 12 + 14 + 12) × 8 = 416 sq ft.
- Subtract openings. Each standard window is about 15 sq ft. Each door is about 21 sq ft. Two windows and one door = 51 sq ft. Paintable area: 416 − 51 = 365 sq ft.
- Divide by coverage. Most interior latex covers 350–400 sq ft per gallon on smooth walls. At 350 sq ft/gal: 365 ÷ 350 = 1.04 gallons per coat.
- Multiply by coats. Two coats is standard. 1.04 × 2 = 2.09 gallons. Round up — buy 3 gallons to have touchup paint available.
Coverage by Paint Type
Not all paint covers the same area. Thicker paints and primers spread less per gallon. Use the coverage rate on the label, or reference these averages:
| Paint Type | Coverage (sq ft/gal) | Best For |
|---|---|---|
| Interior Latex (flat/eggshell) | 350–400 | Walls, ceilings, bedrooms |
| Interior Latex (semi-gloss) | 350–400 | Kitchens, bathrooms, trim |
| Exterior Latex | 250–350 | Siding, stucco, wood exteriors |
| Primer (standard) | 200–300 | New drywall, bare wood, stain blocking |
| Paint + Primer (2-in-1) | 300–400 | Repaints over similar colors |
| Chalk / Specialty Paint | 150–200 | Furniture, accent walls, crafts |
Textured walls (orange peel, knockdown, stucco) reduce coverage by 20–30%. If your walls have heavy texture, lower the coverage setting from 350 to 250–280 sq ft/gal.
How Many Coats of Paint Do You Need?
Two coats is the standard for most paint jobs. One coat rarely gives full coverage unless you're repainting the exact same color. Here's when to adjust:
- 1 coat: Same color repaint using high-quality paint + primer combo. Touchups on small areas.
- 2 coats: Standard for most jobs. Color changes within the same family (light blue to light green). Required for even sheen.
- 3 coats: Dark-to-light color changes (navy to white). Red, yellow, or orange pigments that cover poorly. New drywall that absorbs the first coat.
Always primer first if going from dark to light. A tinted primer (gray for dark finish colors, white for light) saves you a full coat of expensive topcoat paint.
Room-by-Room Estimation Tips
Every room has different challenges. Use these rules of thumb to refine your estimates:
- Bedrooms (12×12): ~2 gallons for 2 coats. Typically 2 windows, 1 door, 1 closet door.
- Living rooms (14×18): ~3 gallons for 2 coats. Often have more windows and an open wall to a hallway.
- Bathrooms (8×6): ~1 gallon for 2 coats. Small area, but use semi-gloss for moisture resistance.
- Kitchens: Count only the wall area not covered by cabinets or backsplash. Usually 30–50% less paintable area than the raw dimensions suggest.
- Hallways: Long and narrow — measure the actual wall length, not the floor area. A 20-foot hallway with 8-foot ceilings has 320 sq ft of wall (both sides).
Paint Cost Comparison (2025–2026)
Paint quality directly affects coverage, durability, and how many coats you need. Cheap paint often costs more in the long run because it takes 3 coats instead of 2.
| Tier | Price per Gallon | Coverage | Example Brands |
|---|---|---|---|
| Budget | $20–$30 | 250–350 sq ft/gal | Glidden, ColorPlace, Dutch Boy |
| Mid-Range | $30–$50 | 350–400 sq ft/gal | Behr, Valspar, HGTV Home |
| Premium | $50–$80 | 350–400 sq ft/gal | Benjamin Moore, Sherwin-Williams, Farrow & Ball |
For a typical 3-bedroom house needing 10–12 gallons: budget paint runs $200–$360, mid-range $300–$600, and premium $500–$960. The premium paint often needs fewer coats and lasts 8–10 years vs 4–5 for budget.
Related Calculators
Planning exterior work too? Use the fence cost split calculator to divide shared fence costs with your neighbor. If you're painting as part of a renovation, the bill split calculator can help split contractor costs between roommates or co-owners.