Curtains & Windows

Curtain Fabric Calculator

Estimate fabric length for paired curtains using fullness, usable fabric width, drops, hems, and repeat.

Window-treatment worksheet

Enter the opening and treatment measurements for Curtain Fabric Calculator

Method for this tool

What the Curtain Fabric Calculator actually calculates

Track width times fullness is divided by fabric width and rounded up to whole widths. Each cut drop is finished length plus hem allowance plus the entered pattern allowance, and fabric length is widths times cut drop. The pattern input is simply added; the engine does not round cuts to exact repeat multiples, match half-drops, or enforce equal-width paired panels.

The calculation path

Finished curtain width determines total fabric widths; each cut drop includes hem and pattern allowance.

Inputs that can change the answer

Track or rod width: Enter track or rod width in m.
Finished curtain length: Enter finished curtain length in m.
Fabric width: Enter fabric width in m.
Fullness multiplier: Flat fabric width divided by track width; use the heading maker’s recommended ratio.
Hem allowance per drop: Add the heading and bottom hem lengths needed for each cut drop, in metres.
Pattern repeat allowance: Enter the extra matching allowance per drop agreed with the workroom. This length is added, not rounded to repeat multiples.

Checks that stay outside the formula

Pattern matching can consume more fabric than a plain cloth; verify the exact repeat.

A practical order for entering the data

Measure track width and the desired finished curtain drop in metres.
Enter usable fabric width, the chosen fullness multiplier, and the combined hem allowance per drop.
Enter a pattern allowance per drop and check the calculated fabric widths against your panel-making plan.

Project walkthrough: Curtains: from window measurement to fabric order

Project walkthrough: Compare blinds and curtains from the same window measurements

Engine check using the prefilled sample

Window-treatment example: track or rod width = 2.2 m, finished curtain length = 2.4 m, fabric width = 1.4 m, fullness multiplier = 2, hem allowance per drop = 0.35 m and pattern repeat allowance = 0.25 m. Replace the sample opening and fabric or hardware values with measurements taken for the mounting method you plan to use.

Results for these inputs

Fabric widths: 4 widths
Cut drop: 3.00 m
Fabric required: 12.00 m

Project-specific method

Worked example and purchase checks

Required finished width comes from track width multiplied by fullness. The calculator turns that width into whole fabric widths, then calculates each drop from finished length plus hem allowance and pattern-repeat allowance.

Illustrative worked example

Full-length patterned curtains on a 2.45 m track using 1.37 m fabric at 2.2× fullness.

Exact inputs for this example

Track or rod width	2.45 m
Finished curtain length	2.35 m
Fabric width	1.37 m
Fullness multiplier	2.2
Hem allowance per drop	0.4 m
Pattern repeat allowance	0.32 m

Fabric widths: 4 widths
Cut drop: 3.07 m
Fabric required: 12.28 m

How to read the result

Use the result to understand the scale of the fabric order. Before purchase, confirm usable fabric width, repeat direction, heading construction, and whether the workroom wants additional matching allowance.

Assumptions this example makes

Fabric width is the usable cut width for the chosen fabric.
One fullness factor and one finished drop length apply to the pair/set.

What this calculator does not prove

Heading style, side hems, joining method, pattern matching across widths, shrinkage, lining, and railroaded fabric can change the order.
Pattern repeat allowance here is simplified; verify the workroom method for expensive patterned fabric.

Curtain measuring pointsSketch is explanatory, not to scale.

Mistakes that change this result

Measuring the window glass instead of the installed track/rod.
Using finished curtain width where the form expects track width.
Ordering the exact calculated length without checking fabric faults or matching method.