Room Paint Calculator
How to Use the Room Paint Estimator
To get a highly accurate estimate of your required paint, grab a tape measure and follow these simple steps:
Windows: Count your windows. The tool will automatically deduct an average of 15 square feet per window so you aren't overbuying paint for glass space.
Length (ft): Measure the longest wall in your room from corner to corner and enter the total feet.
Width (ft): Measure the shorter intersecting wall from corner to corner and input the number.
Ceiling Height (ft): Measure from the floor baseboard straight up to the ceiling line. Standard rooms are usually 8 or 9 feet tall.
Doors: Count the number of standard doors in the room. The calculator will automatically subtract roughly 20 square feet of paintable area per door.
Introduction
Starting a home makeover is exciting, but figuring out exactly how much paint to paint a room can easily become the most frustrating part of the project. Buy too little, and you are rushing back to the hardware store halfway through your second coat with the risk of mismatched dye lots. Buy too much, and you are wasting money on expensive gallons that will just sit drying out in your garage for the next decade.
Our free interior paint calculator removes the guesswork completely. Instead of doing the complicated math yourself, simply input your room's dimensions and the number of standard obstacles (like doors and windows), and this tool will instantly output your net wall area and the exact number of gallons you need for a professional, two-coat finish.
How Many Sq Ft Will a Gallon of Paint Cover?
If you are doing manual calculations before heading to the hardware store, here is the quick industry standard:
- Textured Walls: If your walls have heavy texture (like knockdown or orange peel) or are unprimed drywall, they will absorb more liquid, dropping coverage down to roughly 250 square feet per gallon.
- 1 Gallon of Paint: Covers approximately 350 to 400 square feet for a single coat on a smooth surface.
- Two-Coat Standard: Because most vibrant or color-changing projects require two coats, one gallon effectively covers about 175 to 200 square feet of finished wall.
Frequently Asked Questions
Q. How much paint do I need for a bedroom?
A. For an average 12x12 foot bedroom with an 8-foot ceiling, you have about 384 square feet of wall space before factoring in a door and a window. You will generally need two gallons of paint to comfortably apply two coats to a standard bedroom.
Q. Does this wall paint calculator include the ceiling?
A. No. This specific tool calculates the perimeter wall area only. Ceilings often require a specialized flat ceiling paint to hide imperfections and reduce glare. To paint a ceiling, simply multiply the room's length by its width to find the square footage, then divide by 350 to find the gallons needed.
Q. Why does the tool calculate for two coats automatically?
A. While many modern premium paints advertise "one-coat coverage," professional painters almost universally apply two coats. A second coat ensures true color depth, eliminates roller marks, and provides a much more durable, washable finish.
Planning your next project? Browse our master hub of Free DIY Home & Garden Calculators to get instant material lists, spacing math, and budget estimates.