Understanding Your Benjamin Moore Paint Calculation
Estimating the amount of paint and primer you'll need for a project is crucial for a smooth and successful painting experience. This calculator helps you determine your requirements based on room dimensions, number of doors and windows, desired coats, and the coverage rate of your chosen Benjamin Moore products.
How the Calculation Works
The calculator breaks down the process into several steps:
Wall Surface Area: We first calculate the total surface area of the walls. This is done by summing the areas of all four walls: (Length x Height) + (Width x Height) + (Length x Height) + (Width x Height), which simplifies to 2 * (Room Length + Room Width) * Room Height.
Deductions for Doors and Windows: We then subtract the approximate surface area taken up by doors and windows. While precise measurements aren't always necessary for a quick estimate, we use a simplified input for the amount of paint *per opening* to account for these areas, as precise area calculation for each can be cumbersome.
Net Paintable Area: This is the total wall area minus the area accounted for by doors and windows.
Total Paint Needed: The net paintable area is then divided by the specified paint coverage per gallon. This result is multiplied by the number of coats you plan to apply, giving you the total gallons of paint required.
Total Paint Gallons = (Net Paintable Area / Paint Coverage) * Number of Coats
Total Primer Needed: Similarly, if you are priming, the net paintable area is divided by the primer's coverage per gallon. This calculation typically assumes one coat of primer.
Total Primer Gallons = Net Paintable Area / Primer Coverage
Total Gallons: The sum of the estimated paint gallons and primer gallons provides a total quantity to purchase, ensuring you have enough for the job.
Important Considerations:
Coverage Varies: The coverage rate (square feet per gallon) can differ between Benjamin Moore paint lines and even colors. Always check the product's technical data sheet for the most accurate coverage. Textured surfaces or porous materials may also absorb more paint, reducing coverage.
Multiple Coats: For optimal color depth, coverage, and durability, most projects benefit from two coats of paint. Deep or vibrant colors may require more.
Primer Use: Primer is essential for covering dark or bold colors, painting over glossy surfaces, covering stains, and ensuring better adhesion for your topcoat, especially on new drywall.
Waste Factor: It's always a good idea to purchase a little extra paint than calculated to account for touch-ups, spills, or unforeseen issues. This calculator provides a close estimate, but a small buffer is recommended.
Ceilings and Trim: This calculator focuses on wall area. If you are painting ceilings or trim, you'll need to calculate those areas separately.
Using this tool will help you buy the right amount of paint and primer, minimizing waste and ensuring you have a sufficient supply to achieve a beautiful, professional finish with your Benjamin Moore products.
function calculatePaintNeeds() {
var length = parseFloat(document.getElementById('roomLength').value);
var width = parseFloat(document.getElementById('roomWidth').value);
var height = parseFloat(document.getElementById('roomHeight').value);
var numDoors = parseInt(document.getElementById('numDoors').value);
var numWindows = parseInt(document.getElementById('numWindows').value);
var coats = parseInt(document.getElementById('coatsOfPaint').value);
var paintCoverage = parseFloat(document.getElementById('paintCoverage').value);
var primerCoverage = parseFloat(document.getElementById('primerCoverage').value);
var gallonsPerDoor = parseFloat(document.getElementById('paintGallonsPerDoor').value);
var gallonsPerWindow = parseFloat(document.getElementById('paintGallonsPerWindow').value);
var paintResultDiv = document.getElementById('paintResult');
var primerResultDiv = document.getElementById('primerResult');
var totalGallonsDiv = document.getElementById('totalGallons');
// Clear previous results and styles
paintResultDiv.innerText = "– Gallons of Paint –";
primerResultDiv.innerText = "– Gallons of Primer –";
totalGallonsDiv.innerText = "– Total Gallons –";
paintResultDiv.style.color = "#28a745";
primerResultDiv.style.color = "#28a745";
totalGallonsDiv.style.color = "#28a745";
// Input validation
if (isNaN(length) || length <= 0 ||
isNaN(width) || width <= 0 ||
isNaN(height) || height <= 0 ||
isNaN(numDoors) || numDoors < 0 ||
isNaN(numWindows) || numWindows < 0 ||
isNaN(coats) || coats <= 0 ||
isNaN(paintCoverage) || paintCoverage <= 0 ||
isNaN(primerCoverage) || primerCoverage <= 0 ||
isNaN(gallonsPerDoor) || gallonsPerDoor < 0 ||
isNaN(gallonsPerWindow) || gallonsPerWindow < 0) {
alert("Please enter valid positive numbers for all dimensions, coats, coverage, and gallons per opening.");
return;
}
// Calculate wall area
var wallArea = 2 * (length + width) * height;
// Calculate area to deduct for doors and windows using simplified gallon input
var doorAreaDeduction = numDoors * gallonsPerDoor;
var windowAreaDeduction = numWindows * gallonsPerWindow;
// Net paintable area in square feet
// For simplicity, we'll calculate the paint/primer needed directly
// based on the effective paintable area implicitly derived from gallon inputs.
// If we were to strictly deduct area, it would be:
// var netPaintableArea = wallArea – (doorAreaDeduction * paintCoverage) – (windowAreaDeduction * paintCoverage);
// However, the prompt suggests using 'gallons per door/window', which implies a more direct calculation.
// Let's adjust to calculate total gallons directly.
// Calculate paint gallons needed
var paintGallonsNeeded = (wallArea / paintCoverage) * coats;
// Subtract equivalent paint from doors/windows if they were meant to be deducted from area.
// However, the prompt phrasing "gallons per door/window" suggests these are direct subtractions of paint volume, not area.
// For a more standard approach, we calculate total required based on wall area first.
// Let's assume the "gallons per door/window" represents an amount of paint *saved* or *not needed* because those areas aren't painted.
// This interpretation makes the input values more intuitive for users who might think in terms of paint volume savings.
// Simplified approach: Calculate paint for walls, then subtract savings for openings.
var totalWallPaintGallons = (wallArea / paintCoverage) * coats;
var paintToSubtractForOpenings = (doorAreaDeduction + windowAreaDeduction); // This represents gallons saved
var finalPaintGallons = totalWallPaintGallons – paintToSubtractForOpenings;
// Ensure paint gallons doesn't go below zero
if (finalPaintGallons < 0) finalPaintGallons = 0;
// Calculate primer gallons needed (assuming one coat)
var totalWallPrimerGallons = wallArea / primerCoverage;
// Primer is typically applied to the entire wall area before paint, so we don't subtract for openings in the same way.
// Primer is applied to cover the surface, regardless of openings. The paint then covers the primer.
// The "gallons per door/window" inputs are more relevant for paint calculations.
// If a user wanted to *not prime* openings, that's a different calculation.
// For a standard full primer coat, we use the full wall area.
var finalPrimerGallons = totalWallPrimerGallons;
// Ensure primer gallons doesn't go below zero
if (finalPrimerGallons < 0) finalPrimerGallons = 0;
// Round up to the nearest whole gallon for paint and primer
var paintGallonsRounded = Math.ceil(finalPaintGallons);
var primerGallonsRounded = Math.ceil(finalPrimerGallons);
var totalGallonsRounded = paintGallonsRounded + primerGallonsRounded;
// Display results
paintResultDiv.innerText = paintGallonsRounded + " Gallons";
primerResultDiv.innerText = primerGallonsRounded + " Gallons";
totalGallonsDiv.innerText = totalGallonsRounded + " Gallons";
// Add a warning if calculated paint is very low or zero
if (finalPaintGallons <= 0.1) {
paintResultDiv.innerText += " (Minimal paint needed)";
paintResultDiv.style.color = "#ffc107"; // Warning yellow
}
if (finalPrimerGallons <= 0.1) {
primerResultDiv.innerText += " (Minimal primer needed)";
primerResultDiv.style.color = "#ffc107"; // Warning yellow
}
if (totalGallonsRounded === 0) {
totalGallonsDiv.innerText = "0 Gallons (No paint/primer needed based on inputs)";
totalGallonsDiv.style.color = "#6c757d"; // Muted color for zero result
}
}