Converting square footage (area) to linear footage (length) is a standard calculation in construction and home improvement, particularly when purchasing materials like lumber, decking, flooring, or trim. While square footage represents the total surface area, linear footage represents the total length of the boards needed to cover that area.
The Conversion Formula
To convert square feet to linear feet, you must know the width of the material you are installing. Since board width is commonly measured in inches and area in square feet, you first need to align the units.
Linear Feet = Square Footage ÷ (Board Width in Inches ÷ 12)
Alternatively, if your board width is already in feet:
Linear Feet = Square Footage ÷ Board Width in Feet
Step-by-Step Calculation Example
Let's say you are installing hardwood flooring in a room that is 500 square feet. You have chosen planks that are 5 inches wide.
Convert Width to Feet: Divide the 5-inch width by 12 to convert it to feet. 5 ÷ 12 = 0.4167 feet
Divide Area by Width: Divide the total square footage by the width in feet. 500 ÷ 0.4167 = 1,200 Linear Feet
Result: To cover 500 sq ft with 5-inch wide boards, you need 1,200 linear feet of material (before waste).
Why Include a Waste Factor?
In construction, you never order the exact net amount required. You must account for:
Cuts and Trimming: Pieces cut off at the end of rows.
Defects: Knots, warping, or cracks in wood.
Mistakes: Installation errors.
For standard flooring or decking projects, a 5% to 10% waste factor is standard. For complex patterns (like herringbone flooring) or running material diagonally, professionals recommend adding 15% to 20%.
Applications for This Calculator
This calculation applies to various materials sold by the linear foot but installed over an area:
Decking: determining how many composite or wood deck boards are needed.
Flooring: Buying hardwood or tongue-and-groove planks.
Siding: Estimating lap siding requirements.
Roofing: Calculating metal roofing panel lengths.
Lumber: General carpentry projects.
function calculateLinearFeet() {
// 1. Get Input Values
var sqFtStr = document.getElementById("sqFtInput").value;
var widthStr = document.getElementById("boardWidth").value;
var widthUnit = document.getElementById("widthUnit").value;
var wasteStr = document.getElementById("wasteFactor").value;
var priceStr = document.getElementById("pricePerLf").value;
// 2. Parse and Validate
var sqFt = parseFloat(sqFtStr);
var width = parseFloat(widthStr);
var waste = parseFloat(wasteStr);
var price = parseFloat(priceStr);
// Validation: Ensure we have positive numbers for area and width
if (isNaN(sqFt) || sqFt <= 0) {
alert("Please enter a valid Square Footage greater than 0.");
return;
}
if (isNaN(width) || width 0) {
totalCost = totalLinearFeet * price;
showCost = true;
}
// 8. Update UI
// We use Math.ceil for total linear feet as you usually can't buy fractions of a foot easily,
// or at least standard rounding is safer for ordering. However, for precision, we'll do 2 decimals.
document.getElementById("netResult").innerHTML = netLinearFeet.toFixed(2) + " LF";
document.getElementById("wasteResult").innerHTML = wasteAmount.toFixed(2) + " LF (" + waste + "%)";
document.getElementById("totalResult").innerHTML = Math.ceil(totalLinearFeet) + " LF";
// Show/Hide Cost Row
var costRow = document.getElementById("costRow");
if (showCost) {
document.getElementById("costResult").innerHTML = "$" + totalCost.toFixed(2);
costRow.style.display = "flex";
} else {
costRow.style.display = "none";
}
// Show Results Box
document.getElementById("resultsBox").style.display = "block";
}