Paint Calculator

Follow these steps to calculate the paint needed for your room:

1. Measure and enter your room length in feet. Use a tape measure along the longest wall of the room. If the room is not perfectly rectangular, measure the longest dimension.
2. Measure and enter your room width in feet. Measure the wall perpendicular to the length.
3. Enter the wall height. Standard ceiling height in most homes is 8 feet, but older homes may have 9 or 10-foot ceilings. Measure from floor to ceiling to be accurate.
4. Count and enter the number of doors. Each standard interior door occupies approximately 20 square feet of wall space that does not need wall paint. Include all doors in the room, whether they lead to hallways, closets, or other rooms.
5. Count and enter the number of windows. Each standard window is estimated at approximately 15 square feet. If your windows are significantly larger, such as picture windows or sliding glass doors, you may want to count each large opening as two windows for a more accurate deduction.
6. Select the number of coats. Two coats are standard for most interior painting projects and provide the best balance of color richness, durability, and coverage. One coat may suffice for touch-ups or when painting a similar color. Three coats are recommended for dramatic color changes.

The results display total paint needed in gallons, total wall area, coverable area after deducting openings, and the number of 1-gallon cans to purchase. Always round up to the nearest whole can, and consider buying a small amount extra for future touch-ups.

A paint calculator helps you determine exactly how much paint you need before heading to the store, saving both money and time. The amount of paint required for any project depends on several factors, with the most important being the total paintable surface area and the number of coats you plan to apply. A standard gallon of interior latex paint covers approximately 350 to 400 square feet per coat on smooth drywall, though actual coverage varies based on several conditions.

Surface texture is one of the biggest factors affecting paint coverage. Smooth, primed drywall allows paint to spread efficiently and achieves coverage near the top of the rated range. Rough or textured surfaces like stucco, brick, or heavily textured drywall absorb more paint and may only yield 250 to 300 square feet per gallon. Unprimed or porous surfaces such as new drywall, bare wood, or patched areas also absorb significantly more paint, which is why applying a primer coat first is recommended for these surfaces.

Color changes also affect how much paint you need. Painting a light color over a similar light color may only require one coat for acceptable coverage. However, painting a light color over a dark wall, or applying a bold, saturated color, typically requires two or even three coats to achieve uniform coverage without the old color bleeding through. Using a tinted primer that matches your new color can reduce the number of topcoats needed.

Paint comes in different finish types that suit different applications. Flat or matte finishes hide imperfections well and are popular for ceilings and low-traffic rooms. Eggshell and satin finishes offer a slight sheen and are easier to clean, making them ideal for living rooms and bedrooms. Semi-gloss and high-gloss finishes are durable and moisture-resistant, commonly used for kitchens, bathrooms, trim, and doors. The finish you choose does not significantly affect coverage rates, but higher-gloss paints show surface imperfections more readily, so wall preparation becomes more important.

The paint calculator uses the following formulas to estimate paint needs:

• Room Perimeter = 2 × (Length + Width)
• Total Wall Area = Perimeter × Wall Height
• Door Area = Number of Doors × 20 sq ft (standard door size)
• Window Area = Number of Windows × 15 sq ft (standard window size)
• Paintable (Coverable) Area = Total Wall Area − (Door Area + Window Area)
• Gallons per Coat = Paintable Area ÷ 350 (based on standard coverage rate)
• Total Gallons Needed = Gallons per Coat × Number of Coats
• Cans Needed = Total Gallons rounded up to the nearest whole number

The coverage rate of 350 square feet per gallon is a conservative estimate suitable for smooth drywall. For rough or textured surfaces, you may want to reduce this to 300 square feet per gallon by purchasing additional paint.

Example 1 — Single Room (Bedroom): A bedroom measuring 12 ft × 10 ft with 8-foot ceilings, 2 doors, and 2 windows, painted with 2 coats. Perimeter = 2 × (12 + 10) = 44 ft. Total wall area = 44 × 8 = 352 sq ft. Door area = 2 × 20 = 40 sq ft. Window area = 2 × 15 = 30 sq ft. Paintable area = 352 − 70 = 282 sq ft. Gallons per coat = 282 ÷ 350 = 0.806. Total gallons = 0.806 × 2 = 1.61 gallons. You would purchase 2 one-gallon cans, leaving some extra for touch-ups.

Example 2 — Multiple Rooms (Living and Dining): You want to paint two connected rooms the same color. Room 1 is 18 ft × 14 ft with 9-foot ceilings, 1 door, and 4 windows. Room 2 is 14 ft × 12 ft with 9-foot ceilings, 2 doors, and 2 windows. Room 1: Perimeter = 2 × (18 + 14) = 64 ft. Wall area = 64 × 9 = 576 sq ft. Openings = (1 × 20) + (4 × 15) = 80 sq ft. Paintable = 496 sq ft. Room 2: Perimeter = 2 × (14 + 12) = 52 ft. Wall area = 52 × 9 = 468 sq ft. Openings = (2 × 20) + (2 × 15) = 70 sq ft. Paintable = 398 sq ft. Combined paintable area = 496 + 398 = 894 sq ft. Total gallons for 2 coats = (894 ÷ 350) × 2 = 5.11 gallons. Purchase a 5-gallon bucket plus 1 extra gallon, or 6 individual gallon cans.

Example 3 — Exterior Painting: Painting the exterior of a house with walls measuring approximately 160 linear feet of perimeter and 10-foot wall height. Total wall area = 160 × 10 = 1,600 sq ft. The house has 2 doors and 12 windows. Opening area = (2 × 20) + (12 × 15) = 220 sq ft. Paintable area = 1,600 − 220 = 1,380 sq ft. Exterior paint typically covers about 300 sq ft per gallon on textured siding. Gallons per coat = 1,380 ÷ 300 = 4.6 gallons. For 2 coats: 4.6 × 2 = 9.2 gallons. Purchase two 5-gallon buckets (10 gallons total) to ensure you have enough with a small reserve.