Estimate the amount of paint needed for your next home decor project.
Total Surface Area: 0 sq ft
Paint Required: 0 Gallons
Estimated Quarts: 0 Quarts
*Estimation includes deductions for standard doors (20 sq ft) and windows (15 sq ft).
How to Calculate Paint for Your Room
Planning a home decor update starts with knowing exactly how much material you need. Buying too much paint is a waste of money, while buying too little can lead to inconsistent colors if you have to return to the store for a different batch mix. Our Paint Calculator takes the guesswork out of your DIY project.
The Paint Calculation Formula
To calculate the amount of paint required, we use the following steps:
Step 1: Wall Perimeter – Calculate the total distance around the room (Length + Width) × 2.
Step 2: Gross Wall Area – Multiply the perimeter by the wall height.
Step 3: Deductions – Subtract the area of openings. On average, a door is 20 square feet and a standard window is 15 square feet.
Step 4: Surface Multiplier – Multiply the net area by the number of coats (usually 2 for best coverage).
Step 5: Final Volume – Divide the total surface area by the paint's coverage rate (standard paint covers roughly 350-400 sq ft per gallon).
Realistic Example
Suppose you have a bedroom that is 12 feet long, 10 feet wide, with 8-foot ceilings. You have one door and two windows, and you want to apply two coats of premium paint.
Perimeter: (12 + 10) × 2 = 44 feet
Gross Area: 44 × 8 = 352 sq ft
Deductions: (1 door × 20) + (2 windows × 15) = 50 sq ft
Net Area for 1 Coat: 352 – 50 = 302 sq ft
Total Area for 2 Coats: 302 × 2 = 604 sq ft
Total Paint: 604 / 350 ≈ 1.73 Gallons
Tips for Professional Results
When using this calculator, consider the texture of your walls. Highly textured walls (like popcorn or heavy lace) have more surface area and can require up to 20% more paint. Additionally, if you are painting a light color over a dark color, you may need a third coat or a dedicated primer coat to ensure the old color doesn't bleed through.
function calculatePaint() {
var length = parseFloat(document.getElementById("roomLength").value);
var width = parseFloat(document.getElementById("roomWidth").value);
var height = parseFloat(document.getElementById("wallHeight").value);
var coats = parseFloat(document.getElementById("numCoats").value);
var doors = parseFloat(document.getElementById("numDoors").value);
var windows = parseFloat(document.getElementById("numWindows").value);
var coverage = parseFloat(document.getElementById("paintCoverage").value);
if (isNaN(length) || isNaN(width) || isNaN(height) || isNaN(coats) || isNaN(coverage)) {
alert("Please enter valid numbers for length, width, height, coats, and coverage.");
return;
}
// Calculate total perimeter
var perimeter = 2 * (length + width);
// Calculate gross wall area
var grossArea = perimeter * height;
// Subtract doors and windows
// Avg door = 20 sqft, Avg window = 15 sqft
var doorArea = doors * 20;
var windowArea = windows * 15;
var netAreaPerCoat = grossArea – (doorArea + windowArea);
if (netAreaPerCoat < 0) netAreaPerCoat = 0;
// Total area based on coats
var totalSurfaceArea = netAreaPerCoat * coats;
// Calculate gallons
var gallons = totalSurfaceArea / coverage;
// Calculate quarts (4 quarts in a gallon)
var quarts = gallons * 4;
// Display results
document.getElementById("totalArea").innerHTML = totalSurfaceArea.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("gallonsNeeded").innerHTML = gallons.toFixed(2);
document.getElementById("quartsNeeded").innerHTML = quarts.toFixed(2);
document.getElementById("paintResult").style.display = "block";
}