Curtain guide
How to measure for curtains before buying panels.
Curtain size is based on the rod and finished look, not just the glass. Plan return, stack space, fullness, and drop before comparing prices.
Start with the finished look
The most common curtain mistake is measuring only the window glass and buying panels that barely cover it. Curtains usually look and work better when the rod extends beyond the frame. This lets open panels stack off the glass, makes the window feel wider, and gives the closed curtains enough fabric to hang in folds.
Before measuring, decide whether the curtains should sit inside the frame, just outside the frame, near the ceiling, at the sill, below the sill, or to the floor. That decision controls the numbers you enter into the calculator.
| Measurement | What it means | Planning note |
|---|---|---|
| Window width | The visible opening or frame width. | Use this as the base, then add return on each side. |
| Side return | Extra rod width beyond the window. | 6-10 inches per side is common for many medium windows. |
| Fullness | Fabric width divided by rod width. | 2x is a common balanced starting point. |
| Drop | Finished curtain length from rod to endpoint. | Choose sill, apron, floor, break, or puddle length before buying. |
| Panel width | The finished width of one panel. | Ready-made panels use finished width, not bolt width. |
Measuring sequence
- Measure the window or frame width.
- Choose how far the rod should extend beyond each side.
- Add the side returns to get rod width.
- Pick fullness based on style, fabric weight, and budget.
- Measure from rod height to the desired endpoint.
- Divide target fabric width by finished panel width and round up.
Ready-made panels versus custom fabric
Ready-made curtain panels are usually sold by finished width and finished length. Custom curtains often start with fabric yardage, seam allowance, hems, pattern repeat, lining, and workroom rules. The calculator can help with early planning for both, but final buying details depend on how the curtains will be made.
If the fabric has a large repeat, extra yardage may be needed so patterns align across panels. If blackout lining or interlining is added, cost and weight increase. Hardware should also be included in the budget: rods, brackets, rings, hooks, and anchors are separate purchases.