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The Window Edit · Practical Design Guide
How to measure for curtains - and make them look custom.
Exact width, graceful length, and thoughtful placement matter more than the price of the fabric. Use this guide to plan each measurement before you order.
Calculate my curtain size →
Before you begin
Measure the installation - not only the glass.
The most common mistake is measuring the window and buying curtains of the same width. That produces panels that look flat when closed and expose too much glass when open.
Instead, plan the rod first. Its usable width determines how much fabric you need, while its mounting height determines the finished curtain length.
Your five-minute measuring kit
Metal tape measurePencil and paperStep stoolLevel or laser levelA second person for wide windows
The complete formula
Four decisions, in the correct order.
- 01
Measure the window width
Measure from the outside edge of the left trim to the outside edge of the right trim. Record the number in inches. If the window has no trim, measure the full opening.
Do not include handles, finials, or decorative rod ends. - 02
Choose the rod extension
Add approximately 6 to 12 inches on each side when wall space allows. More extension exposes more glass when the curtains are open and can make the window feel broader.
Window width+Left extension+Right extension=Rod width - 03
Choose your fullness
Multiply the usable rod width by the fullness that suits your fabric and desired look. Sheer or lightweight fabric can carry more fullness; bulky fabric may need less.
1.5×Relaxed2×Tailored & generous2.5×Full & dramatic - 04
Calculate panel quantity
Divide the total fabric width required by the finished width of one panel, then round up to the next whole panel - or the next even number when you want equal panels on both sides.
Rod width × fullness÷One panel’s finished width=Panels needed
Choose the finish before measuring down
Where should the curtain end?
Measure from the exact point where the curtain will hang on the rod or track - not automatically from the top of the rod. Rings, clips, pockets, and hooks all change the starting point.
Worked example
A 60-inch window, measured properly.
Assume a 60-inch-wide window, 8 inches of rod extension on each side, 2× fullness, and panels that are 50 inches wide.
- 01
60 + 8 + 8 = 76 inchesplanned rod width
- 02
76 × 2 = 152 inchestotal fabric width needed
- 03
152 ÷ 50 = 3.04round up to four panels for an even pair
Result: four 50-inch panels create 200 inches of fabric across a 76-inch rod - about 2.6× fullness. If that feels fuller than desired, look for wider two-panel sets or custom widths rather than rounding down to skimpy coverage.
The expensive-looking difference
Seven mistakes to avoid.
- Buying panels before choosing the rod position
- Matching total curtain width to the window width
- Mounting the rod directly on the upper trim
- Choosing a rod that ends at the window frame
- Forgetting that finials need additional wall clearance
- Measuring length from the wrong point on the hardware
- Assuming every floor or ceiling is perfectly level
Save before shopping
Your window measurement card
- Window width
- ________ in.
- Rod extension
- Left ____ / Right ____
- Planned rod width
- ________ in.
- Mounting height
- ________ in.
- Finished length
- ________ in.
- Fullness
- 1.5× / 2× / 2.5×
- Panel width
- ________ in.
- Panel quantity
- ________ panels
Use your browser’s print option to save this card
Skip the arithmetic
Turn your measurements into a complete window plan.
The complimentary calculator recommends rod width, mounting height, curtain length, fullness, panel width, and quantity - plus personalized designer notes.
Open the curtain calculator →Frequently asked questions
The details people measure twice.
How wide should curtains be for a window?
As a practical starting point, the combined finished width of the curtain panels should be about 1.5 to 2.5 times the width of the space the fabric will cover. Two times fullness creates a reliably tailored, generous look for many fabrics.
How far should a curtain rod extend past the window?
Extending the rod roughly 6 to 12 inches beyond the window frame on each side often lets the open curtains sit mostly outside the glass. Use the room, available wall space, finials, and panel stack-back to refine the number.
How high should I hang a curtain rod?
Hang the rod above the window trim rather than directly on it. A position about 4 to 8 inches above the frame works in many rooms; mounting closer to the ceiling can visually lengthen the wall when proportions allow.
Should curtains touch the floor?
For a polished everyday installation, choose a finished length that just kisses the floor or floats about half an inch above it. A deliberate 1- to 3-inch break feels relaxed; a larger puddle is decorative but requires more upkeep.
Do I measure the window or the curtain rod?
Measure the window first to plan rod placement. Once the rod width is established, use the rod's usable width - not including decorative finials - to calculate the total fabric width and panel quantity.
Continue your room plan