Calculating the right amount of fabric for your curtains is crucial to avoid waste or insufficient material. This calculator helps you determine the total fabric yardage (or meterage) required based on your curtain dimensions and desired fullness.
Key Measurements and Concepts:
Fabric Width: The width of the fabric as it comes off the roll. Standard widths vary, often around 140-150 cm for home furnishings.
Fabric Length per Panel: The length of a single piece of fabric you'll cut.
Finished Curtain Height: The final desired height of your curtain from the rod or track to the hem.
Finished Curtain Width: The final desired width of your curtain panel.
Pleat Factor (Fullness): This determines how much fabric is used to create folds or pleats.
A pleat factor of 1.5 means you need 1.5 times the finished width of the curtain in fabric for the pleating. This gives about 50% fullness.
A pleat factor of 2.0 (or higher) means you need twice (or more) the finished width in fabric, creating richer, fuller pleats (100% fullness).
Seam Allowances: Extra fabric needed for hemming the sides and bottom, and for joining panels if necessary.
Horizontal Seam Allowance: For side hems and potentially for joining fabric panels.
Vertical Seam Allowance: For the bottom hem and the top if not using a heading tape/grommet allowance.
Heading Allowance: Extra fabric needed at the top for the curtain heading tape, rod pocket, or grommets.
How the Calculation Works:
The calculator determines the fabric needed in two main stages:
Fabric Length per Panel:
This is calculated based on the finished curtain height, adding allowances for the top heading and the bottom hem.
Total Panel Length = Finished Curtain Height + Heading Allowance + Vertical Seam Allowance (Bottom Hem)
This value should ideally not exceed your purchased Fabric Length per Panel. If it does, you'll need to adjust your design or fabric choice.
Fabric Width per Panel:
This is determined by the finished curtain width, the pleat factor, and the horizontal seam allowances.
Required Fabric Width = (Finished Curtain Width * Pleat Factor) + (2 * Horizontal Seam Allowance per edge)
This calculation assumes the *finished* curtain width already accounts for any center split.
Number of Panels Needed:
We then figure out how many panels of fabric, with the specified Fabric Width, are needed to achieve the Required Fabric Width per panel.
Number of Panels = Ceiling(Required Fabric Width / Fabric Width)
The ceiling function ensures we round up to the nearest whole number of panels.
Total Fabric Length:
Finally, the total fabric required is the length needed for each panel multiplied by the number of panels.
Total Fabric Length = Total Panel Length * Number of Panels
Total Fabric Area:
While the calculator primarily outputs length, the conceptual area can be thought of as:
Total Fabric Area = Total Fabric Length * Fabric Width (of the roll)
However, for purchasing, Total Fabric Length is the most practical metric.
Example Usage:
Let's say you want to make a pair of curtains for a window:
Finished Curtain Height: 240 cm
Finished Curtain Width (per panel): 75 cm (for a total of 150 cm width for the pair)
Pleat Factor: 1.5 (for 50% fullness)
Fabric Width: 140 cm
Horizontal Seam Allowance: 3 cm (per side edge)
Vertical Seam Allowance (Bottom Hem): 10 cm
Heading Tape Allowance: 7 cm
Calculation Steps:
Total Panel Length: 240 cm (Height) + 7 cm (Heading) + 10 cm (Hem) = 257 cm
Required Fabric Width per Panel: (75 cm * 1.5) + (2 * 3 cm) = 112.5 cm + 6 cm = 118.5 cm
Number of Panels: Ceiling(118.5 cm / 140 cm) = Ceiling(0.846…) = 1 panel (Note: This might seem low, but this calculator assumes you input the width *per panel*. If you were calculating for a pair of curtains and dividing the total width, you'd get different results. For a single panel of 75cm finished width, one panel of 140cm fabric is usually enough to achieve 1.5x fullness.)
Total Fabric Length Required: 257 cm (Length per panel) * 1 panel = 257 cm
Therefore, you would need approximately 257 cm of fabric from a 140 cm wide roll. You would cut one piece of fabric 257 cm long from the roll.
Important Consideration: If your required fabric width per panel exceeds the fabric roll width, you will need to join multiple widths of fabric together. The calculation for the number of panels handles this by rounding up. Always buy slightly more fabric than calculated to account for pattern matching, errors, or unexpected shrinkage.
function calculateFabric() {
var fabricWidth = parseFloat(document.getElementById("fabricWidth").value);
var fabricLengthPerPanel = parseFloat(document.getElementById("fabricLengthPerPanel").value);
var curtainHeight = parseFloat(document.getElementById("curtainHeight").value);
var curtainWidth = parseFloat(document.getElementById("curtainWidth").value);
var pleatFactor = parseFloat(document.getElementById("pleatFactor").value);
var seamAllowanceHorizontal = parseFloat(document.getElementById("seamAllowanceHorizontal").value);
var seamAllowanceVertical = parseFloat(document.getElementById("seamAllowanceVertical").value);
var headingTapeOrGrommets = parseFloat(document.getElementById("headingTapeOrGrommets").value);
var resultDiv = document.getElementById("result");
resultDiv.style.backgroundColor = "var(–success-green)"; // Reset color
if (isNaN(fabricWidth) || fabricWidth <= 0 ||
isNaN(fabricLengthPerPanel) || fabricLengthPerPanel <= 0 ||
isNaN(curtainHeight) || curtainHeight <= 0 ||
isNaN(curtainWidth) || curtainWidth <= 0 ||
isNaN(pleatFactor) || pleatFactor < 1 || // Pleat factor must be at least 1
isNaN(seamAllowanceHorizontal) || seamAllowanceHorizontal < 0 ||
isNaN(seamAllowanceVertical) || seamAllowanceVertical < 0 ||
isNaN(headingTapeOrGrommets) || headingTapeOrGrommets fabricLengthPerPanel) {
resultDiv.innerHTML = "Required panel length (" + totalPanelLengthRequired.toFixed(1) + " cm) exceeds fabric panel length (" + fabricLengthPerPanel.toFixed(1) + " cm). Adjust inputs or fabric.";
resultDiv.style.backgroundColor = "#dc3545"; // Error color
return;
}
// Calculate the total width of fabric needed for one panel, including fullness and side hems
var requiredFabricWidthPerPanel = (curtainWidth * pleatFactor) + (2 * seamAllowanceHorizontal);
// Calculate the number of panels needed based on fabric roll width
// Use Math.ceil to round up to the nearest whole number of panels
var numberOfPanels = Math.ceil(requiredFabricWidthPerPanel / fabricWidth);
// If required width is less than fabric width, we still need at least 1 panel
if (numberOfPanels === 0 && requiredFabricWidthPerPanel > 0) {
numberOfPanels = 1;
} else if (numberOfPanels === 0 && requiredFabricWidthPerPanel <= 0) {
numberOfPanels = 0; // Handle cases where curtain width might be zero or negative (though input validation should prevent this)
}
// Calculate the total fabric length required
var totalFabricLength = totalPanelLengthRequired * numberOfPanels;
// Ensure total fabric length is not negative or zero if inputs were valid but resulted in 0 panels
if (totalFabricLength 0 || headingTapeOrGrommets > 0 || seamAllowanceVertical > 0)) {
totalFabricLength = totalPanelLengthRequired; // At least one panel's length is needed if height/allowances are positive
numberOfPanels = 1; // Force at least one panel if calculated length is positive
} else if (totalFabricLength <=0) {
totalFabricLength = 0; // If all dimensions are effectively zero, result is zero
numberOfPanels = 0;
}
var resultHtml = "Total Fabric Length Needed: " + totalFabricLength.toFixed(1) + " cm";
resultHtml += "Number of Fabric Panels Required: " + numberOfPanels + "";
// Add a note if multiple fabric widths need to be joined
if (numberOfPanels > 1 && fabricWidth < requiredFabricWidthPerPanel) {
resultHtml += "(Note: You will need to join multiple widths of fabric)";
}
resultDiv.innerHTML = resultHtml;
}