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A Paint Calculator is an essential tool for DIY home renovators and professional painters alike. It helps you determine exactly how much paint you need to buy for a specific room, preventing you from overspending on excess gallons or running out of paint halfway through your project.
How the Paint Calculation Works
To calculate paint requirements, you must first determine the total square footage of your walls. You then subtract the areas that will not be painted (like doors and windows) to find your net paintable area.
- Total Wall Area: Add the length and width of the room, multiply by 2 (to get the perimeter), and then multiply by the wall height.
- Exclusions: A standard interior door accounts for about 21 square feet, and a standard window accounts for about 15 square feet. Subtract these from your total wall area.
- Coverage: A standard gallon of interior paint typically covers about 350 to 400 square feet. This calculator uses a conservative estimate of 350 square feet per gallon to ensure you have enough paint for the job.
How to Use This Tool
- Enter the Length, Width, and Height of your room in feet.
- Input the number of standard doors and windows in the room. The calculator will automatically subtract their square footage so you aren't calculating paint for glass or wood.
- Specify the Number of Coats. Most color changes require at least two coats for proper coverage and durability.
- Review your Gallons Required on the main dashboard. If the number is a decimal (like 1.4 gallons), you will need to purchase 2 full gallons or 1 gallon plus a couple of quarts.
Frequently Asked Questions
How much paint do I need for the ceiling?
This calculator is designed for painting walls. If you also plan to paint the ceiling, you need to calculate its area separately (Length × Width) and divide by 350. Because ceilings are highly absorbent, you may need slightly more paint for a ceiling than a standard primed wall.
Do I need to prime the walls first?
If you are painting over a dark color with a lighter color, repairing drywall, or painting bare wood, you should use a primer first. You can use this exact same calculator to determine how many gallons of primer you will need; simply set the "Number of Coats" to 1.
What if my room is an irregular shape?
If your room is not a simple rectangle, you should break the walls down individually. Measure the length of each wall, add all those lengths together to get the total perimeter, and multiply by the ceiling height. You can then enter that total perimeter as the "Length", set the "Width" to 0, and use the calculator normally.