Paint Calculator: Wall, Ceiling & Room Paint Estimator
Use this paint calculator to determine exactly how much paint and primer your room requires before heading to the home center. This estimator accounts for room perimeter, wall height, doors, windows, optional ceilings, two-coat application, and a practical 10% roller waste margin so you never run out mid-wall.
Buy 2 gallons + 1 quart (or round up to 3 gallons for touch-ups).
| Gross Wall Area | 416 sq ft |
|---|---|
| Openings Deductions (1 door, 2 windows) | −50 sq ft |
| Net Base Surface Area | 366 sq ft |
| Coated Area (2 coats) | 732 sq ft |
| Area with 10% Waste Margin | 805.2 sq ft |
📐 Show Formula and Default Assumptions
We believe all home improvement estimates should be transparent and verifiable. Below is the exact math running in this browser tool:
-
Wall Area Formula:
Gross Wall Area = 2 × (Length + Width) × HeightCalculates continuous wall perimeter multiplied by ceiling height. -
Standard Door Deduction:
Deduction = Doors Count × 20 sq ft (1.9 m²)Accounts for standard 32" × 80" or 36" × 80" interior door openings. Fully editable. -
Standard Window Deduction:
Deduction = Windows Count × 15 sq ft (1.4 m²)Represents standard 36" × 60" double-hung windows. Fully editable. -
Paint Coverage Rate:
350 sq ft per gallon (8.6 m² per liter)Manufacturer average on smooth, pre-primed drywall. Textured plaster or unprimed drywall absorbs more. -
Application Waste & Roller Absorption:
Gross Paint = Net Paint × (1 + Waste% / 100)10% covers roller-nap saturation, tray residue, edging cuts, and future touch-up jars.
Note: All default assumptions (waste %, coverage rates, container yields) can be adjusted directly in the input fields above to match your project specifications.
How to Accurately Measure a Room for Paint
- Measure the floor perimeter: Run a tape measure flat along the baseboards from corner to corner. Record the room length and width in feet or meters.
- Measure the ceiling height: Measure vertically from floor to ceiling at two corners. If ceilings vary, use the tallest point.
- Count openings to deduct: Tally every door and window. Standard doors occupy roughly 20 sq ft (1.9 m²); standard double-hung windows occupy roughly 15 sq ft (1.4 m²).
- Decide on the ceiling: If you plan to paint the ceiling in the same wall color, toggle the ceiling option. If painting the ceiling flat white, calculate it as a separate surface.
- Inspect surface texture: Smooth pre-painted drywall yields approximately 350 to 400 sq ft per gallon. Porous bare drywall, heavy orange peel texture, or masonry surfaces require roughly 20% to 30% more paint.
How the Paint Calculation Works (Worked Example)
Here is an actual step-by-step calculation for an everyday 14 ft by 12 ft bedroom with standard 8 ft ceilings, 1 door, and 2 windows:
- 1. Gross Wall Area: 2 × (14 + 12) × 8 = 2 × 26 × 8 = 416 sq ft.
- 2. Deductions: 1 door (20 sq ft) + 2 windows (2 × 15 = 30 sq ft) = 50 sq ft total deductions.
- 3. Net Wall Area per coat: 416 - 50 = 366 sq ft.
- 4. Two-Coat Application: 366 × 2 = 732 sq ft of total coverage.
- 5. 10% Waste & Roller Allowance: 732 × 1.10 = 805.2 sq ft.
- 6. Gallons Required: 805.2 ÷ 350 = 2.30 gallons.
- 7. What to Buy: 2 one-gallon cans plus 2 quarts, OR round up to 3 one-gallon cans for better cost efficiency (since 2 quarts often cost 85% of a full gallon).
Paint Coverage & Can Size Quick-Reference Guide
| Container Size | Typical Coverage (1 Coat) | Typical Coverage (2 Coats) | Best Used For |
|---|---|---|---|
| 1 Quart (0.95 L) | 85 - 100 sq ft | 40 - 50 sq ft | Accent walls, doors, trim, small bathrooms |
| 1 Gallon (3.79 L) | 350 - 400 sq ft | 175 - 200 sq ft | Average bedroom walls or small kitchen |
| 2 Gallons (7.57 L) | 700 - 800 sq ft | 350 - 400 sq ft | Standard 12x14 master bedroom (2 coats) |
| 5 Gallon Pail (18.9 L) | 1,750 - 2,000 sq ft | 875 - 1,000 sq ft | Open-concept living rooms, entire basements, new homes |
Frequently Asked Questions About Paint Calculator
How many square feet does one gallon of paint cover?
One gallon of quality interior latex paint covers between 350 and 400 square feet on previously painted, smooth drywall. If painting porous raw drywall, rough masonry, or heavily textured walls, coverage drops to 250 to 300 square feet per gallon.
Do I really need two coats of paint?
Yes, almost always. Even "one-coat guarantee" paints produce a more uniform sheen, deeper color saturation, and better scuff resistance with two coats. A second coat covers thin spots, roller tracks, and edge cut-in variances.
Should I buy quarts or round up to another full gallon?
When your estimate calls for 2.2 to 2.4 gallons, it is usually cheaper or nearly the same price to buy 3 full gallons instead of 2 gallons plus 2 individual quarts. Buying the extra gallon also guarantees an exact factory color match and leaves touch-up paint for scuffs.
Do I need primer, and how much should I buy?
You need a dedicated primer if painting bare drywall, patching joint compound, transitioning from a dark color to light, or covering water and smoke stains. Primer covers roughly 300 sq ft per gallon because bare surfaces absorb more liquid.
How do I store leftover paint for future touch-ups?
Transfer leftover paint into a clean, airtight container (like a mason jar or touch-up bottle) to minimize headspace air. Label it with the room name, paint brand, sheen, formula sticker, and date. Store in a climate-controlled room away from freezing temperatures.