Paint Coverage Calculator
Quickly determine how many gallons of paint you need for any room by entering its dimensions, door and window count, and desired number of coats.
What is Paint Coverage?
A paint coverage calculator helps homeowners, contractors, and DIY enthusiasts determine exactly how much paint to purchase before starting a painting project. Buying too little paint means extra trips to the store and potential color-matching problems between batches. Buying too much wastes money and leaves you with cans of unused paint to store or dispose of. The calculation works by first determining the total wall surface area of a room based on its perimeter and height. It then subtracts non-paintable surfaces like doors (approximately 21 square feet each for a standard 3x7 foot door) and windows (approximately 15 square feet each for a standard 3x5 foot window). The remaining paintable area is then multiplied by the number of coats you plan to apply. Most interior latex paints cover approximately 350 square feet per gallon on smooth, primed surfaces. Coverage can vary depending on surface texture, paint quality, color change (dark to light requires more coats), and application method. Rough or textured surfaces like stucco or brick may reduce coverage by 25-50 percent. For best results, always buy slightly more than the calculated minimum. This calculator rounds up to the nearest whole gallon since paint is sold in full gallons, and having a small amount of leftover paint is useful for future touch-ups. Professional painters typically recommend keeping at least a quart of each color for repairs and touch-ups after the job is complete. The number of coats depends on several factors: the existing wall color, the new color being applied, paint quality, and whether a primer was used. Most projects require two coats for even coverage and proper color development. Going from a dark color to a light one may require three coats or a tinted primer coat first.
How to Calculate
- Measure the length and width of the room in feet
- Measure the wall height from floor to ceiling
- Count the number of standard doors in the room
- Count the number of standard windows in the room
- Select how many coats of paint you plan to apply (2 is standard)
- Review the results showing total wall area, paintable area, and gallons needed
Formula
Perimeter = 2 x (Length + Width) Total Wall Area = Perimeter x Wall Height Paintable Area = Total Wall Area - (Doors x 21 sq ft) - (Windows x 15 sq ft) Gallons Needed = ceiling((Paintable Area x Number of Coats) / 350) Where 21 sq ft is a standard door (3 ft x 7 ft), 15 sq ft is a standard window (3 ft x 5 ft), and 350 sq ft is the average coverage per gallon of interior latex paint.
Example Calculation
A room that is 12 ft long, 10 ft wide, and 8 ft tall with 1 door and 2 windows, painted with 2 coats: Perimeter = 2 x (12 + 10) = 44 ft Total Wall Area = 44 x 8 = 352 sq ft Door area = 1 x 21 = 21 sq ft Window area = 2 x 15 = 30 sq ft Paintable Area = 352 - 21 - 30 = 301 sq ft Paint needed = (301 x 2) / 350 = 1.72 gallons, rounded up to 2 gallons
Frequently Asked Questions
How much area does one gallon of paint cover?
One gallon of standard interior latex paint covers approximately 350 square feet on smooth, primed surfaces. Textured walls, unprimed surfaces, or porous materials may reduce coverage to 250-300 square feet per gallon.
Should I count closet doors as doors?
Yes, count any standard-sized door that you will not be painting. If you plan to paint the closet doors the same color as the walls, do not subtract them from the paintable area.
Do I really need two coats of paint?
In most cases, yes. Two coats provide even color, better coverage of the old color, improved durability, and a more uniform finish. You may get away with one coat if you are painting the same color over itself or using a high-quality paint-and-primer combination.
Does this calculator account for ceiling paint?
No, this calculator covers wall area only. To calculate ceiling paint, multiply room length by room width to get the ceiling area, then divide by 350 to determine additional gallons needed.
What if my windows or doors are not standard size?
This calculator uses standard sizes (3x7 ft doors, 3x5 ft windows). For large picture windows or French doors, you can count them as 2 windows or 2 doors respectively to better approximate the unpainted area.
Should I add extra paint for touch-ups?
The calculator rounds up to the nearest gallon, which typically provides enough extra for minor touch-ups. For a large project, buying an additional quart is a good practice for future repairs.