Paint Calculator
Estimate exactly how much paint you need for walls, ceilings, and rooms. Accounts for multiple coats, doors, windows, and paint coverage rates with optional cost estimation.
Room Dimensions
What to Paint
Doors & Windows
(Deducted from total)Standard door: 3 ft × 7 ft = 21 sq ft
Standard window: 3 ft × 5 ft = 15 sq ft
Door Dimensions
Door area: 21.0 sq ft each (3 × 7)
Window Dimensions
Window area: 15.0 sq ft each (3 × 5)
Paint Details
Can Size & Cost
(Optional)Paint Estimate
For a 12 ft × 10 ft room with 8 ft walls, the total wall area is 352 sq ft. After deducting 51 sq ft for doors and windows, the paintable area is 301 sq ft. With 2 coats, you need to cover 602 sq ft — requiring approximately 1.72 gallons of paint.
How much paint do your walls actually need?
Buying paint is one of those tasks where a rough guess often leaves you either running back to the store mid-project or storing half-used cans for years. Our paint calculator does the precise math — enter your room dimensions, account for doors and windows, choose how many coats you want, and get an instant estimate in gallons or liters, plus how many cans to buy and the total cost.
Whether you’re refreshing a bedroom, repainting an entire house, or tackling a ceiling, the process is the same: measure, subtract the openings, multiply by coats, and let the numbers guide your purchase.
How to calculate paint coverage by hand
If you want to understand the math behind the numbers, here’s the straightforward process:
- Find the wall perimeter. Add all four wall lengths together.
Perimeter = Length₁ + Width₁ + Length₂ + Width₂
- Calculate total wall area. Multiply perimeter by wall height.
Wall Area = Perimeter × Wall Height
- Subtract doors and windows. Each standard door is about 21 sq ft; a standard window is about 15 sq ft.
Paintable Area = Wall Area − (Doors × 21) − (Windows × 15)
- Multiply by number of coats. Two coats is the standard recommendation.
Total Paintable Area = Paintable Area × Number of Coats
- Divide by coverage rate. Most paint covers 350–400 sq ft per gallon.
Paint Needed (gal) = Total Area ÷ Coverage Rate
Example: A 12 ft × 10 ft room with 8 ft walls, 1 door, 2 windows, and 2 coats:
- Perimeter = 12 + 10 + 12 + 10 = 44 ft
- Wall area = 44 × 8 = 352 sq ft
- Subtract openings: 352 − 21 − 30 = 301 sq ft paintable
- With 2 coats: 301 × 2 = 602 sq ft total
- Paint needed: 602 ÷ 350 = 1.72 gallons → 2 gallons
Understanding paint coverage rates
Coverage varies by paint type, surface texture, and application method. Here’s what to expect:
| Surface Type | Coverage (sq ft/gal) | Why |
|---|---|---|
| Smooth, previously painted | 350–400 | Best-case scenario, sealed surface |
| New drywall | 250–300 | Porous surface absorbs more paint |
| Textured walls | 200–300 | Texture creates more surface area |
| Stain-blocked areas | 200–250 | Primer layer adds resistance |
| Rough masonry/brick | 150–200 | Highly porous, uneven surface |
Pro tip: Always check the paint can label. Manufacturers print the exact coverage rate for that specific product, and it’s more accurate than any general estimate.
One coat vs. two coats
The number of coats you need depends on what you’re painting over:
- One coat works for: touch-ups, painting the same color over the same color, or using a high-quality paint-and-primer combo on a well-prepared surface.
- Two coats is the standard for: new colors over existing colors, raw drywall with primer, and most quality finishes. Two coats gives you better coverage, richer color, and a more durable surface.
- Three coats is needed for: very dark to very light transitions, certain deep or vivid colors, and specialty finishes like lacquer or high-gloss.
Tips for buying and applying paint
- Buy 10% extra. Touch-ups, edges, and roller absorption eat into your coverage. Running out mid-wall is far more expensive than storing a leftover quart.
- Buy all paint at once. Color can vary between batches (called “lot variation”). Mixing two cans from different stores may produce a visible difference on the wall.
- Don’t forget the primer. New drywall, stains, or dramatic color changes need primer first. It seals the surface and reduces how many topcoats you need.
- Store leftover paint properly. Seal the can tightly and keep it in a cool, dry place. Properly stored latex paint lasts 2–3 years for touch-ups.
Planning a larger renovation?
Paint is just one piece of the puzzle. If your project also involves flooring, tiling, or concrete work, these calculators can help you plan the full scope:
- Tile Calculator — Estimate tiles for floors or walls
- Grout Calculator — Calculate grout for your tile installation
Frequently Asked Questions
Common questions about this calculator.
How much paint do I need for a room?
To calculate paint needed for a room, measure the total wall area (perimeter × height), subtract doors and windows, then divide by the paint coverage rate (typically 350–400 sq ft per gallon). For a standard 12×12 ft room with 8 ft walls, you’ll need about 1.5 gallons for two coats. Our paint calculator does this math instantly—just enter your room dimensions, number of doors and windows, and desired coats for a precise estimate in gallons or litres.
How do I measure a room for paint?
Measure the length and width of the room in feet, then calculate the perimeter by adding all four wall lengths. Multiply the perimeter by the wall height to get the total wall area. Subtract the area of doors (about 21 sq ft each) and windows (about 15 sq ft each) to find the paintable surface. This gives you the square footage needed for your paint estimate. Our paint calculator automates this process for quick, accurate results.
How much paint should I buy?
Always buy 10% more paint than your calculated estimate to account for roller absorption, touch-ups, and uneven application. Purchase all paint for a project at once to avoid color variations between batches. For a typical room, one to two gallons will cover most walls with two coats. Check the paint can label for the exact coverage rate—different paints cover different square footage per gallon, affecting how many cans you need.
How many gallons of paint do I need?
A gallon of interior paint typically covers 350–400 square feet on smooth surfaces. To find gallons needed, divide your total paintable area (including multiple coats) by the coverage rate. For example, a 400 sq ft wall area with two coats requires about 2 gallons. Rough or new surfaces may need more paint. Our paint calculator converts square footage into exact gallons and suggests how many cans to purchase.
How much paint do I need for a ceiling?
Calculate ceiling paint by measuring the length × width of the room. A standard 12×12 ft ceiling is 144 sq ft. Most ceilings need one to two coats—one is often sufficient since ceilings experience less wear. Divide the ceiling area by the paint coverage rate (350–400 sq ft/gallon). For 144 sq ft, you’ll need roughly 0.4 gallons for one coat. Our paint calculator includes ceiling estimates when you select the ceiling option.
How do I estimate a paint job?
Start by measuring all surfaces to be painted—walls, ceilings, trim. Calculate the area, subtract doors and windows, then multiply by the number of coats. Divide by the paint’s coverage rate to find gallons needed. Factor in primer if painting new drywall or making a dramatic color change. Add 10% for waste. Our paint calculator automates these steps, providing instant estimates for interior paint, exterior paint, and cost projections.
How much does it cost to paint a room?
Paint costs vary by quality and brand. Interior latex paint ranges from $20–$50 per gallon. A typical 12×12 ft room needs about 1.5–2 gallons for two coats, so paint alone costs $30–$100. Premium paints may cost more but offer better coverage. Don’t forget primer ($15–$30 per gallon) if needed. Our paint calculator includes a cost estimation feature—enter your paint price per gallon to see total material costs instantly.
How much exterior paint do I need?
Exterior paint coverage depends on surface texture—smooth siding covers 350–400 sq ft/gallon, while rough stucco may cover only 150–200 sq ft/gallon. Measure the total exterior wall area, subtract large openings like garage doors, and multiply by coats. Exterior projects often need primer and two topcoats. Our paint calculator handles exterior measurements, accounting for different surface types and providing accurate gallon estimates for your home’s exterior.
How many coats of paint do I need?
Most interior walls need two coats for optimal coverage, color richness, and durability. One coat may suffice for touch-ups, painting the same color, or using paint-and-primer combos on prepared surfaces. Three coats are needed for dramatic color changes (dark to light), deep colors, or specialty finishes. New drywall always requires primer plus two coats. Our paint calculator lets you select the number of coats to refine your paint estimate.
What affects paint coverage rates?
Paint coverage depends on surface texture, paint quality, and application method. Smooth, previously painted surfaces yield 350–400 sq ft/gallon. New drywall absorbs more, reducing coverage to 250–300 sq ft/gallon. Textured walls, porous masonry, or stained surfaces may cover only 150–250 sq ft/gallon. Always check the paint can label for the manufacturer’s coverage rate—it’s the most accurate number for your specific paint. Our paint calculator uses these rates for precise estimates.
Should I use a paint calculator or estimate by hand?
A paint calculator saves time and reduces errors by automating measurements, accounting for doors, windows, multiple coats, and varying coverage rates. Manual estimates often miss details, leading to under- or over-buying paint. Our paint calculator provides instant results in gallons or litres, suggests how many cans to purchase, and includes cost estimates—making it the most reliable way to plan your painting project efficiently.