Deductions: "+doorDeduction+" (Doors) + "+windowDeduction+" (Windows) = "+(doorDeduction+windowDeduction)+" sq ft
Net Area per Coat: "+netArea.toFixed(2)+" sq ft
Total Area for "+c+" coats: "+totalCoverageNeeded.toFixed(2)+" sq ft";document.getElementById('stepDetails').innerHTML=detailText;document.getElementById('stepDetails').style.display='block';}else{document.getElementById('stepDetails').style.display='none';}}
How to Use the Paint Calculator
Estimating the amount of paint required for a home improvement project is essential to avoid unnecessary trips to the hardware store or wasting money on excess supplies. This paint calculator helps you determine exactly how many gallons of paint you need based on the dimensions of your room and the number of openings like doors and windows.
To get an accurate result, follow these steps:
- Room Dimensions
- Measure the length and width of the floor, and the height of the walls from floor to ceiling.
- Openings (Doors & Windows)
- Count the number of standard doors (approx. 21 sq ft each) and windows (approx. 15 sq ft each) to subtract them from the total wall area.
- Coverage Rate
- Most standard paints cover roughly 350 to 400 square feet per gallon. Check your paint can for the specific manufacturer's rating.
- Number of Coats
- Usually, two coats are recommended for a professional, even finish, especially when changing colors.
The Math Behind the Calculation
When using the paint calculator, we apply a standard geometric formula to find the surface area of your walls. For a standard four-walled room, the formula is:
Total Surface Area = [(2 × (Length + Width)) × Height] − Deductions
- Perimeter: (2 × (Length + Width)) calculates the total distance around the room.
- Gross Area: Perimeter multiplied by Height gives the total area if there were no doors or windows.
- Deductions: We subtract 21 sq ft per door and 15 sq ft per window as a standard industry average.
- Gallons: (Net Area × Coats) / Coverage per Gallon.
Calculation Example
Scenario: You want to paint a bedroom that is 12 feet long, 10 feet wide, with 8-foot ceilings. The room has 1 door and 2 windows, and you plan on applying 2 coats of paint.
Step-by-step solution:
- Calculate Perimeter: 2 × (12 + 10) = 44 feet
- Calculate Gross Area: 44 × 8 = 352 sq ft
- Total Deductions: (1 × 21) + (2 × 15) = 51 sq ft
- Net Area: 352 – 51 = 301 sq ft
- Total Surface to Paint (2 coats): 301 × 2 = 602 sq ft
- Gallons Needed (at 350 sq ft/gal): 602 / 350 = 1.72 Gallons
In this case, the paint calculator suggests buying 2 gallons of paint to ensure you have enough for the job and some left over for future touch-ups.
Common Questions
How much does 1 gallon of paint cover?
On average, a gallon of quality interior paint covers between 350 and 400 square feet. However, porous surfaces like new drywall or textured walls may absorb more paint, reducing coverage to about 250-300 square feet per gallon.
Do I need to calculate for the ceiling?
If you are painting the ceiling the same color as the walls, add (Length × Width) to your total area. Most people use a specific flat white ceiling paint, which should be calculated separately using the "Single Wall" mode with the length and width of your floor as the dimensions.
Should I buy 1-gallon cans or a 5-gallon bucket?
If your paint calculator result is over 4 gallons, buying a 5-gallon bucket is usually more cost-effective. Additionally, "boxing" your paint (mixing multiple cans together) ensures color consistency across the entire project.