Paint Calculator
Instantly estimate exactly how many gallons of paint you need for a bedroom, 12×12 room, or your whole house, plus calculate the total material cost.
Whether you are repainting a small bathroom, figuring out how much paint for a bedroom, or estimating an entire exterior job, buying the correct amount of paint is essential. Buy too little, and you interrupt your workflow to run to the hardware store. Buy too much, and you waste money on heavy buckets that will sit unused in your garage.
Our paint calculator takes the guesswork out of your project. By entering your room dimensions (or square footage), we instantly subtract non-paintable obstacles like doors and windows, factor in your desired number of coats, and tell you exactly how many gallons you need to purchase.
How to Calculate How Much Paint You Need
To accurately estimate your paint needs, you must find the “net paintable surface area” and divide it by the paint’s standard coverage rate. Here is the exact mathematical process used by professional painters:
- Find Gross Wall Area: If measuring a room, multiply the length by the height, and multiply the width by the height. Add those together, and multiply by 2 (for opposite walls).
Gross Area = (Length × Height × 2) + (Width × Height × 2) - Subtract Deductions: Subtract the square footage of any doors (standard is 21 sq ft) and windows (standard is 15 sq ft) to find your Net Area.
- Factor in Coats: Multiply the Net Area by the number of coats you intend to apply (always plan for 2 coats unless touching up). This gives you the Total Coverage Area.
- Calculate Gallons: Divide the Total Coverage Area by the coverage rate of your specific paint (typically 350 sq ft per gallon).
- Round Up: Because paint is sold in whole gallons, always round up your final decimal figure.
Gallons = ((Net Area × Coats) ÷ Coverage Rate)
How Many Square Feet Does a Gallon of Paint Cover?
A frequent question from DIYers is, “How many square feet does 1 gallon of paint cover?” Understanding coverage rates is the secret to a perfect paint estimate.
A standard 1-gallon can of interior acrylic latex paint covers roughly 350 to 400 square feet for a single coat on a smooth, primed surface.
- Smooth Drywall: ~350 – 400 sq ft per gallon.
- Textured Walls or Stucco: ~250 – 300 sq ft per gallon (texture drastically increases the physical surface area the paint must fill).
- Bare, Unprimed Drywall: The first coat will soak in heavily like a sponge, often yielding only ~200 – 250 sq ft per gallon. Always use a dedicated, cheaper drywall primer first.
How many square feet does 5 gallons of paint cover?
If you are painting a whole house interior or a large exterior, you will likely buy 5-gallon buckets. Since one gallon covers ~350 sq ft, a 5-gallon bucket will cover approximately 1,750 to 2,000 square feet for a single coat.
Room Paint Estimator (10×10 & 12×12 Rooms)
How much paint for a 10×10 room?
A 10×10 bedroom with standard 8-foot ceilings has a gross wall area of 320 sq ft. If we subtract one door (21 sq ft) and one window (15 sq ft), the net area is 284 sq ft.
Because you need two coats for a flawless finish, your total coverage area is 568 sq ft. One gallon (covering 350 sq ft) isn’t enough. You will need to buy 2 gallons of paint for a 10×10 room.
How much paint for a 12×12 room?
“Will 1 gallon of paint cover a 12×12 room?” Let’s do the math. A 12×12 room with 8-foot ceilings has 384 sq ft of gross wall area. Subtracting a door and a window leaves ~348 sq ft of net area.
While 1 gallon will barely cover one single coat (at 350 sq ft/gal), a single coat rarely looks good. For the required two coats, your coverage area is 696 sq ft. Therefore, you must buy 2 gallons of paint for a 12×12 room.
Never Plan for Just One Coat
Unless you are painting over a wall with the exact same color and sheen to hide minor scuffs, always calculate your material based on two coats. Even expensive premium “paint and primer in one” products rarely provide flawless coverage in a single pass over a contrasting color.
Ceiling Paint Calculator Rules
If you are using our tool as a ceiling paint calculator, simply check the “Include ceiling” box in the dimensions mode. The calculator will automatically add the Length × Width of the room to your net area.
Important Note on Ceilings: Ceilings are typically painted with a specialized “flat” ceiling paint. Because ceiling paint is formulated to hide imperfections and is usually very thick and flat, it sometimes has a slightly lower spread rate than satin wall paint. However, calculating ceiling area at 350 sq ft per gallon is still the industry standard.
Painting Cost Calculator Basics
If you are trying to estimate paint cost, the price per gallon varies wildly based on brand, quality, and sheen. A flat builder-grade paint might cost $20, while a premium washable matte from Sherwin Williams or Benjamin Moore can exceed $80 a gallon.
- Economy / Contractor Grade: $20 – $30 per gallon. (Good for quick flips, but often requires more coats to hide old colors).
- Standard Mid-Tier: $35 – $55 per gallon. (The sweet spot for most homeowners).
- Premium / Designer: $60 – $90+ per gallon. (Excellent durability, scrubbability, and rich pigments).
Frequently Asked Questions
Assuming a standard 8-foot ceiling, a 12×12 room has 384 square feet of wall space. Subtracting a door and a window leaves a net area of about 330 square feet. Because you need two coats, the total coverage area is 660 square feet. Therefore, you will need to buy 2 gallons of paint.
A standard gallon of interior acrylic latex paint covers roughly 350 to 400 square feet for a single coat. This assumes the surface is smooth and previously primed or painted. Textured walls will drop coverage to about 250 sq ft per gallon.
Since one gallon covers about 350 to 400 square feet, a 5-gallon bucket of paint will cover approximately 1,750 to 2,000 square feet for a single coat. This is often enough to put two coats on the walls of three average-sized bedrooms.
A 10×10 room with 8-foot ceilings has 320 square feet of gross wall space. After deducting a door and window, you have about 270 square feet to paint. For two coats, you need to cover 540 square feet, meaning you must buy 2 gallons of paint.
To paint exactly 1000 net square feet of wall space with two standard coats, you are covering a total area of 2000 square feet. Divide this by 350 (average coverage per gallon), and you get 5.7 gallons. You will need to purchase 6 gallons of paint.
Reference: https://en.wikipedia.org/wiki/Tile