Paint Area Calculator
Paintable Area
Gallons Needed
Room Paint Diagram
InteractiveHow to Calculate Paint Area in Square Feet
Buying the right amount of paint coverage means calculating the total paintable square footage, subtracting openings like doors and windows, and accounting for multiple coats including a second coat and optional primer. Too little paint forces a mid-project store run (and risks color batch mismatches). Too much paint wastes money and storage space. The waste factor and wall texture also affect how many gallons you'll need. Start by measuring walls with the wall square footage calculator, then the surrounding room area, estimate spend via the price per square foot calculator, or use the main square footage calculator.
Step 1: Calculate Gross Wall Area
Add the lengths of all four walls (perimeter) and multiply by the ceiling height. For a 15×12 ft room with 9 ft ceilings: perimeter = 2(15+12) = 54 ft. Gross wall area = 54 × 9 = 486 sq ft.
Paint Area Formula
FormulaExample: (54 ft × 9 ft) − 45 sq ft openings = 441 sq ft paintable area
Step 2: Subtract Openings
A standard interior door is about 21 sq ft (3×7 ft). A standard window is about 12 sq ft (3×4 ft). Subtract each opening from the gross wall area. Don't skip this — in a room with 2 doors and 3 windows, you'd over-buy by nearly 80 sq ft worth of paint.
Step 3: Multiply by Coats
Most interior painting requires 2 coats for uniform coverage. A second coat ensures even color, especially when changing from dark to light. Primer adds an additional coat for new drywall or drastic color changes. Multiply your net paintable area by the number of coats, then divide by the coverage per gallon (typically 350–400 sq ft for interior paint) to get gallons needed. Consider paint finish too — flat and eggshell finishes cover slightly more than semi-gloss and gloss.
Paint Coverage Reference by Surface Type
Different surfaces absorb paint at different rates. Wall texture, porosity, and material all affect paint coverage. Smooth drywall gives the best coverage per gallon, while porous surfaces like brick and stucco need more exterior paint. Using primer on raw or new surfaces significantly improves coverage and reduces the number of top coats required. Low VOC paint from popular paint brands typically offers similar coverage to standard paint formulations.
| Surface Type | Coverage per Gallon | Notes |
|---|---|---|
| Smooth Drywall | 350–400 sq ft | Best coverage, standard assumption |
| Textured Drywall | 300–350 sq ft | Texture absorbs more paint |
| New/Unprimed Drywall | 250–300 sq ft | Primer coat needed first |
| Wood / Trim | 300–350 sq ft | Grain absorbs paint unevenly |
| Brick / Masonry | 200–300 sq ft | Porous surface, heavy absorption |
| Stucco (Exterior) | 150–250 sq ft | Very rough texture |
| Metal | 350–500 sq ft | Non-porous, good coverage |
| Concrete Floor | 250–350 sq ft | Depends on sealer and porosity |
Paint Coverage Chart
Use this quick-reference chart to estimate how much paint coverage you'll get from different quantities. These figures assume smooth drywall with standard interior paint and one coat. For a second coat, simply double the square footage requirement.
| Paint Amount | Coverage (1 Coat) |
|---|---|
| 1 Quart | 90–100 sq ft |
| 1 Gallon | 350–400 sq ft |
| 2 Gallons | 700–800 sq ft |
| 3 Gallons | 1,050–1,200 sq ft |
| 4 Gallons | 1,400–1,600 sq ft |
| 5 Gallons | 1,750–2,000 sq ft |
| 6 Gallons | 2,100–2,400 sq ft |
| 7 Gallons | 2,450–2,800 sq ft |
| 8 Gallons | 2,800–3,200 sq ft |
| 9 Gallons | 3,150–3,600 sq ft |
| 10 Gallons | 3,500–4,000 sq ft |
Room-by-Room Paint Estimation Guide
Standard Bedroom (12×12 ft, 9 ft ceiling)
Perimeter = 48 ft. Gross wall area = 432 sq ft. Subtract 1 door (21 sq ft) + 2 windows (24 sq ft) = 387 sq ft. With 2 coats and 350 sq ft/gallon coverage per gallon: 387 × 2 ÷ 350 = 2.2 gallons → buy 3 gallons. Choose an eggshell or satin paint finish for bedrooms.
Living Room (15×18 ft, 9 ft ceiling)
Perimeter = 66 ft. Gross wall area = 594 sq ft. Subtract 2 doors + 3 windows = 78 sq ft → 516 sq ft. With a second coat: 516 × 2 ÷ 350 = 2.9 gallons → buy 3 gallons. Add a 4th gallon if painting the ceiling paint (270 sq ft). A satin finish works best for living rooms.
Bathroom (5×8 ft, 8 ft ceiling)
Perimeter = 26 ft. Gross wall area = 208 sq ft. Subtract 1 door + 1 window = 33 sq ft → 175 sq ft. With 2 coats: 175 × 2 ÷ 350 = 1 gallon. Bathrooms need moisture-resistant semi-gloss paint — slightly more expensive per gallon. Consider low VOC paint for better indoor air quality.
Ceilings
Ceiling paint area = room length × width. A 15×12 room has 180 sq ft of ceiling. Ceiling paint is thicker to prevent dripping and typically covers 350–400 sq ft per gallon. Use flat finish ceiling paint to hide imperfections. One gallon with 2 coats handles rooms up to 175 sq ft ceiling area.
Paint Needed By Room Size
Quick reference for estimating paint coverage by room dimensions. These estimates assume 9 ft ceiling paint height, 1 door, 2 windows, and 2 coats of interior paint. Actual needs may vary based on wall texture and paint finish.
| Room Size | Paint Needed |
|---|---|
| 10 × 10 ft | 1 gallon |
| 10 × 12 ft | 1 gallon |
| 12 × 12 ft | 2 gallons |
| 12 × 15 ft | 2 gallons |
| 15 × 15 ft | 2–3 gallons |
| 20 × 20 ft | 4 gallons |
Paint Needed By House Size
Planning a whole-house paint project? These estimates cover all interior paint for walls only (not ceiling paint or trim paint). Add 15–20% for ceiling paint and doors. Actual totals depend on room count, layout, wall texture, and paint finish choice. Most paint brands offer 5-gallon buckets at better per-gallon pricing.
| House Size | Approx Paint |
|---|---|
| 1,000 sq ft | 3 gallons |
| 1,500 sq ft | 5 gallons |
| 2,000 sq ft | 6 gallons |
| 2,500 sq ft | 8 gallons |
| 3,000 sq ft | 10 gallons |
Interior vs Exterior Paint
Choosing between interior paint and exterior paint matters for durability, coverage, cost, and finish. Here's a detailed comparison to help you pick the right product for your project.
Interior Paint
- Coverage: 350–400 sq ft/gallon
- Cost: $25–$50 per gallon
- Durability: 5–10 years
- Coats: 2 coats standard
- Finish options: Flat, Eggshell, Satin, Semi-Gloss, Gloss
- Best for: Bedrooms, kitchens, bathrooms, living rooms
- VOC: Low VOC paint options widely available
Exterior Paint
- Coverage: 250–350 sq ft/gallon
- Cost: $35–$70 per gallon
- Durability: 7–15 years
- Coats: 2–3 coats typical
- Finish options: Flat, Satin, Semi-Gloss
- Best for: Siding, stucco, brick, fences, trim
- Features: UV protection, mildew resistant, weather-proof
| Feature | Interior | Exterior |
|---|---|---|
| Coverage | 350–400 sq ft/gal | 250–350 sq ft/gal |
| Cost | $25–$50/gal | $35–$70/gal |
| Durability | 5–10 years | 7–15 years |
| Coats | 2 | 2–3 |
Paint Cost Estimator
Get a quick estimate of your total paint project cost including materials and labor. Adjust the paint price and labor cost to match local paint brands pricing.
Shopping List
Waste Factor
Many professionals always buy extra paint to account for spills, roller absorption, touch-ups, and surface irregularities. The waste factor is the extra percentage of paint you should add to your calculated amount. Adjust the slider below to see how the waste factor changes your total paint estimate.
Paint Finish Selector
Your paint finish affects durability, washability, and appearance. Choose the right finish for each room based on traffic and moisture levels.
Slight sheen, easy to clean. Best for bedrooms and living rooms.
Best for Bedrooms
Flat or Eggshell — low sheen hides imperfections and creates a calm, cozy feel.
Best for Bathrooms
Semi-Gloss — moisture resistant, easy to wipe down, prevents mildew.
Best for Kitchens
Satin or Semi-Gloss — handles grease and steam well, very washable.
Real Examples
Skip the abstract formulas — here are real-world paint calculations you can apply immediately. Each example shows dimensions, square footage, coats, and final gallons needed.
Coverage Calculator
Enter the number of gallons you have on hand to see how much area they'll cover. Useful for checking if leftover paint is enough for your next project.
Comparison Table
Compare paint finish options by paint coverage and best use. Choose the right paint finish for each surface — from flat for ceiling paint to gloss for trim paint and doors.
Flat
Eggshell
Satin
Semi-Gloss
Gloss
| Paint Type | Coverage | Best Use |
|---|---|---|
| Flat | 400 sq ft | Ceilings |
| Eggshell | 350 sq ft | Bedrooms |
| Satin | 350 sq ft | Living Room |
| Semi-Gloss | 300 sq ft | Kitchen |
| Gloss | 250 sq ft | Trim |
Specialized Square Feet Calculators
Each tool is purpose-built with its own dedicated calculator, visual diagrams, and step-by-step guidance.
Triangle
Find the area of any triangle using base × height or Heron's formula with three side lengths.
Irregular Shape
Break any complex shape into rectangles and triangles. Add sections and sum them automatically.
Inches
Enter measurements in inches and get instant square feet results. Includes a quick-reference conversion table.
From Meters
Convert metric measurements to square feet. Perfect for international real estate and imported materials.
Linear Feet
Convert linear footage to square feet for lumber, carpet, fencing, decking, and rolled materials.
Sq Meters
Convert sq ft to sq m with live dual display. Essential for international real estate and architecture.
Sq Yards
Divide sq ft by 9 to get sq yd. Perfect for carpet ordering, sod purchases, and fabric estimates.
Acres
Convert property area from sq ft to acres. Ideal for land sales, farming, zoning, and lot size comparisons.
Cubic Feet
Add depth to any area to calculate volume. Essential for concrete, mulch, soil, gravel, and pool planning.
House
Add rooms one by one and get your home's total square footage, with a live bar chart breakdown per room.
Room
Measure rectangular or L-shaped rooms for flooring, paint, and renovation budgeting with instant cost estimates.
Wall
Get net wall area for paint, wallpaper, or tile by subtracting doors and windows from the gross surface.
Tile
Enter room size and tile dimensions to calculate tile count, boxes to buy, and total material cost including waste.
Concrete
Get slab area, cubic yards of concrete, bags needed, and pour cost for any project.
Land
Measure any property lot or parcel in sq ft and acres. Supports rectangular, triangular, and irregular shapes.
BTU Calculator
Calculate heating and cooling BTU needs per square foot based on climate zone, ceiling height, and insulation.
Cost
Estimate total project cost from area and price per square foot. Compare scenarios with tax and markup.
Flooring
Find exact flooring material for hardwood, laminate, vinyl, or carpet with waste factor and box count.
Roof
Get true roof surface area using pitch multiplier. Includes roofing squares, shingle bundles, and cost.
Paint Area
Get paintable wall area with door and window deductions. Calculates gallons, coats, and total paint cost.
Estimation
Add multiple areas, apply buffer percentages, and get quick estimates for budgeting any project.
Related Calculators
Explore other free square footage and cost tools:
Frequently Asked Questions
Standard paint coverage is about 350 to 400 square feet per gallon. This means you need roughly 0.0025 to 0.0029 gallons of paint per square foot, or approximately one quart for every 100 square feet of surface area.
To calculate paint by square feet, determine the total paintable surface area (wall height × width, minus any doors and windows), multiply by the number of coats you plan to apply, and divide the total by the paint's coverage rate (typically 350 sq ft per gallon).
To estimate a paint job, calculate the total square footage of all paintable surfaces. For materials, divide the square footage by 350 to determine the gallons of paint needed. For labor, multiply the total square footage by the local contractor rate, which typically ranges from $1.50 to $4.00 per square foot depending on prep work.
A gallon of quality paint can cover between 350 and 400 square feet on smooth, primed surfaces. On porous, textured, or unprimed surfaces like new drywall or brick, coverage decreases to about 250 to 300 square feet per gallon.
The standard coverage of a gallon of paint is 350 to 400 square feet. Textured walls, stucco, concrete, or dry drywall will absorb more paint, reducing the effective coverage rate to around 200 to 300 square feet per gallon.
Measure the length of each wall you want to paint and add them together to get the perimeter of the room. Multiply this perimeter by the ceiling height to find the gross wall square footage. Subtract 21 square feet for each standard door and 12 square feet for each standard window.
Find the total square footage of all walls by multiplying their lengths by heights. Then, subtract the area of any doors, windows, fireplaces, cabinets, or other non-paintable fixtures. The remaining figure is your net paintable wall area.
Calculate the net paintable square footage for each room individually by measuring their walls and subtracting openings. Add these room totals together to get your grand total square footage, multiply by the number of coats, and divide by 350 to find the total gallons of paint required.
Measure the room's perimeter (sum of all wall lengths) and multiply by ceiling height to get gross wall area. Subtract doors and windows. Multiply by number of coats. Divide by 350 sq ft/gallon and round up to the nearest whole gallon.
One gallon covers approximately 350–400 square feet on smooth drywall with one coat. Textured walls, raw wood, or masonry absorb more paint and reduce coverage to 200–300 sq ft per gallon. Always check the manufacturer's label for specific coverage.
A 12×12 room with 9 ft ceilings has ~387 sq ft of paintable wall area (after door/window deductions). With 2 coats: 774 sq ft ÷ 350 = 2.2 gallons. Buy 3 gallons. Add 1 more gallon if you're painting the ceiling too.
Yes. A standard door (21 sq ft) and window (12 sq ft) each save measurable paint. In a small bathroom, skipping the deduction would overestimate by 15–20%. Use 21 sq ft per door and 12 sq ft per standard window as defaults.
Two coats is standard for most interior walls. Use 3 coats when covering dark colors with light paint, painting over patched areas, or using low-coverage colors like reds and yellows. One coat may suffice for touch-ups with matching paint.
Primer is recommended for new drywall, stain-blocking, or drastic color changes. Primer coverage is similar to paint (300–400 sq ft/gallon). Calculate primer separately — it's an additional gallon count on top of your paint coats.
Measure each exterior wall's width and height, sum all wall areas, and subtract windows, doors, and garage openings. Exterior surfaces (siding, stucco, brick) have lower coverage rates — use 250–350 sq ft per gallon depending on texture.
Measure the linear feet of trim and multiply by the trim width (typically 3.5–5.5 inches = 0.3–0.46 ft). A room with 40 linear feet of 4-inch baseboard has 13 sq ft of trim. One quart covers 75–100 sq ft — usually enough for 2 coats of all trim in an average room.
Yes — always buy 5–15% extra paint beyond your calculated amount. Extra paint accounts for touch-ups, spills, roller absorption, and slight miscalculations. Keeping leftover paint also helps with future repairs, ensuring an exact color match without needing to buy a new gallon.
Yes, textured walls use significantly more paint than smooth walls. A textured surface can reduce paint coverage by 15–30%, bringing it down from 350–400 sq ft per gallon to around 250–300 sq ft per gallon. Heavy textures like knockdown or popcorn require even more paint due to the extra surface area created by the texture.
Ceiling paint is calculated separately by multiplying room length × width. A 12×15 ft room has 180 sq ft of ceiling. Ceiling paint is thicker and covers 350–400 sq ft per gallon. With 2 coats, 180 sq ft needs about 1 gallon. Flat or matte ceiling paint is recommended to hide imperfections.
Trim paint is calculated using linear feet × width. Standard baseboards are 3.5–5.5 inches wide. A typical room has 40–50 linear feet of baseboard at 4 inches wide = about 15 sq ft. Window and door trim adds another 10–20 sq ft. One quart of semi-gloss or gloss trim paint covers 75–100 sq ft — usually sufficient for all trim in a standard room with 2 coats.