Curtains & Windows

Curtain Rod Length Calculator

Size a curtain rod beyond the window so curtains can stack clear of the glass.

Window-treatment worksheet

Enter the opening and treatment measurements for Curtain Rod Length Calculator

Method for this tool

What the Curtain Rod Length Calculator actually calculates

Rod length is window width plus two equal side extensions. Overall width adds two equal finial allowances. The engine does not estimate stack-back from fabric weight or fullness and does not choose bracket spacing, support count, or a load-rated rod.

The calculation path

Window width receives an extension on both sides based on panel weight and desired stack-back.

Inputs that can change the answer

Window width: Enter window width in m.
Extension each side: Enter extension each side in m.
Finial allowance each side: Enter finial allowance each side in m.

Checks that stay outside the formula

Check for adjacent walls, cabinets, and switches before extending the rod.

A practical order for entering the data

Measure the window width in metres.
Choose the rod extension on each side after considering curtain stack-back and nearby obstructions.
Enter each finial's additional projection and compare both rod-only and overall widths with the available wall.

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: window width = 1.6 m, extension each side = 0.2 m and finial allowance each side = 0.08 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

Rod excluding finials: 2.00 m
Overall width: 2.16 m

Project-specific method

Worked example and purchase checks

The rod body equals the measured window width plus the chosen extension on both sides. Finial projection is then added on both ends to show the complete wall span required.

Illustrative worked example

A 1.8 m window receives 250 mm of stack-back space on each side and finials projecting 90 mm per end.

Exact inputs for this example

Window width	1.8 m
Extension each side	0.25 m
Finial allowance each side	0.09 m

Rod excluding finials: 2.30 m
Overall width: 2.48 m

How to read the result

Use the rod and overall widths as two different purchase checks. Mark the bracket centres and finial ends on the wall, then compare the selected hardware load and support instructions with the finished curtain.

Assumptions this example makes

Window width is measured on the wall plane used for hardware positioning.
The same extension and finial projection are used on the left and right.
The stated rod length excludes finials, while overall width includes them.

What this calculator does not prove

It does not determine rod diameter, bracket spacing, centre supports, fixing strength, curtain weight, or safe anchoring.
Corners, cabinets, switches, air vents, and asymmetric stack-back space require a separate wall check.

Window, rod body, and overall finial spanSketch is explanatory, not to scale.

Mistakes that change this result

Ordering the overall finial-to-finial width as the adjustable rod-body length.
Measuring glass width instead of the intended hardware span.
Choosing extension without checking how much fabric must stack clear of the opening.